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Diuretics and heart failure: 10 things you need to know
  1. Alex Laver and
  2. Dave Dickson


Background: Diuretics are the cornerstone of heart failure therapy in veterinary medicine, yet their use can cause confusion and concern in practice. To gather material for this article, the authors asked their peers what they most wanted to know about the diagnosis and treatment of congestive heart failure (CHF).

Aim of the article: This article aims to answer some of the most common questions about the use of diuretics in the treatment of CHF.

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Alex Laver qualified from Bristol university in 2015 and spent three years in small animal practice before joining Heart Vets in 2018. She is currently working towards her certificate in advanced veterinary practice (veterinary cardiology) and is involved in research into lung ultrasound and atrial fibrillation.

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Dave Dickson qualified from the Royal Veterinary College in 2004. He is an RCVS-recognised Specialist in cardiology and is a member of the Heart Vets team, a specialist-led cardiology consultancy service for the assessment and treatment of cardiorespiratory problems in veterinary patients.

1. Is my patient in congestive heart failure?

Diagnosing congestive heart failure (CHF) can be challenging, but by breaking the diagnostic process down into a few key points it becomes much easier. Incorporating the following tips into your regular case work-up will soon make them habitual and will help you develop pattern recognition. If you are ever confounded in the middle of a case you think has CHF, go back to the basics – it is amazing how often simple clues have been missed.

Clinical signs

Don’t underestimate the importance of taking a good history. Outward signs often noted by owners include coughing, abdominal distension and dyspnoea; however, delving a little deeper into the history is important.


Is the patient exercising normally? How are they at the end of a walk? Do they play? Reduced activity or struggling towards the end of a walk may indicate reduced cardiac output.


Has the owner noticed any changes in the patient’s breathing? Breathing rate and depth may have changed, the patient may take longer to recover to normal after exercise, or there may have been episodes of open-mouthed breathing or panting.

Weakness or collapse

Has the patient had any episodes of weakness or collapse at home or outside? What were they doing when this happened? A detailed description is key. Weakness or collapse on exertion may be a sign of forward (systolic) failure, and arrhythmia can cause episodes at rest or during excitement. Without a detailed history, these cases are often confused with neurological episodes.


Ask the owner about the duration and severity of any cough and to describe the sound. Are any other animals in the household coughing? A cough may bother the owner more than the patient but it is often the reason for presentation and distinguishing non-cardiac coughing (eg, kennel cough and respiratory disease) is a useful first step. The cough of CHF is typically soft, occurring at rest or overnight, whereas airway collapse coughing is loud and usually occurs when excited or barking.

Weight loss

Does the patient have a good appetite? Rapid weight loss with normal appetite may be an indicator of non-cardiac disease. Acute CHF can cause a decreased appetite, whereas chronic weight loss despite a normal appetite can be a feature of cardiac cachexia.

Parasite prevention

Lungworm should always be a differential diagnosis with respiratory signs. A patient that is up to date with Angiostrongylus vasorum prevention is unlikely to be affected. Some formulations of ‘worming tablets’ only cover for tapeworm not lungworm and owners may not be aware of this. Find out specifically which parasite treatment has been given, and when.

Clinical examination


Feel the apex beat on both sides of the chest with the palms of your hand. A firm apical impulse is more easily felt in slimmer animals but can also be an indicator of cardiomegaly if it is abnormally prominent. Feel for a thrill and if present note where this is most obvious, making sure that, particularly in younger patients, you have felt high up in the axilla and cranially both sides (Fig 1). Thrills are useful auscultation guides and are often missed in cases with congenital disease. Thrills in older patients can indicate advanced valvular disease.

Fig 1: It is important to use your hands as well as your stethoscope in the cardiac clinical examination. Feel over the apex beat and check for thrills, as well as feeling for the femoral pulse quality


  • Heart rate: tachycardia (particularly in large or athletic breeds) where slower rates are expected can be a sign of heart disease. Patients in uncontrolled CHF will usually be tachycardic (providing there is no arrhythmia).

  • Heart rhythm: listen for at least 30 seconds. Is the rhythm regular or irregular? The presence of sinus arrhythmia (regularly irregular) makes CHF less likely. All arrhythmia should be assessed with an electrocardiogram.

  • Lung fields: are lung sounds clear or muffled? Describe the sounds that you hear. Crackles are not specific to heart failure and are often misdiagnosed. If they sound like Velcro unpeeling, this is more likely to be true pulmonary oedema in CHF. Loud crackles (think ‘Rice Krispies’) are heard where there is lower airway disease such as airway collapse or interstitial fibrosis.

Femoral pulses

Bounding, weak or absent femoral pulses are abnormal. Feel for these while auscultating to detect pulse deficits.

Abdominal palpation

Palpate for signs such as pain that may influence heart rate, and feel for any obvious masses. Where suspicious of ascites, check for a fluid wave.

Once you have a detailed history and cardiac-focused clinical examination, you should have more of an idea of the patient’s CHF risk. Thoracic imaging can be considered as the next step.

Thoracic radiography

Always take at least two views: dorsoventral and right lateral are most commonly used in our practice.

A convincing alveolar-interstitial lung pattern, vascular congestion and cardiac enlargement with left atrial enlargement are all key indicators of pulmonary oedema (Fig 2). Lung patterns in the absence of left atrium (LA) enlargement are very unlikely to be left-sided congestive failure. Make sure that radiographs are straight and inflated, as tilted views and under inflation will give falsely large cardiac silhouettes.

Fig 2: (a) Right lateral and (b) dorsoventral radiographs of a dog showing vascular congestion, pulmonary oedema and cardiomegaly in left-sided congestive heart failure


You do not have to be a skilled ultrasonographer to assess for free fluid. Familiarise yourself with the key imaging locations and this can form a vital part of any rapid examination, particularly in an emergency. Carry out TFAST and AFAST (thoracic-/abdominal-focused assessment with sonography for trauma, triage and tracking) to:

  • Identify pleural and/or pericardial effusion within the thorax (TFAST);

  • Look for ascites in the absence of any immediately obvious abdominal cause (eg, mass) (AFAST).

You can also look for the presence of multiple B lines on lung ultrasound. These are a strong indicator for ‘wet lungs’ and in possible CHF are likely to indicate pulmonary oedema (Fig 3).

Fig 3: Lung ultrasound image showing B lines on the lung surface, consistent with pulmonary oedema


Although a detailed Doppler echocardiogram can provide enhanced information about cardiac structure and function, a basic echo will add useful information where CHF is suspected (Fig 4). If you are less confident with echocardiography, assessing LA size is the single most important thing, as most animals with a normal LA will not have left-sided CHF.

Fig 4: Echocardiography. (a) Having two pairs of hands to hold the patient makes a big difference to patient cooperation and ease of scanning. (b) Right parasternal short axis view showing left atrium (LA):aorta (Ao) measurements in a dog with an enlarged left atrium. Taking the average of three measurements helps improve accuracy

Using the combination of history, clinical examination findings and some simple thoracic imaging, reaching a diagnosis of CHF is possible in most patients. Knowing an animal’s risk for being in CHF then helps guide you on why treatment may not be working and gives you more confidence to adjust or stop medication.

2. Do I manage acute and chronic CHF differently?

Although both clinical presentations are managed with diuretics (Table 1), the approach to the acute CHF case focuses on stabilisation before diagnosis. In chronic CHF patients, treatment is fine-tuned by acquiring more detailed information on the case.

Table 1: Diuretic treatment protocol following a congestive heart failure diagnosis

Acute CHF

The aim in the acute CHF case is to treat congestion and support cardiac output. The use of diuretics in these patients is focused on clearing or significantly reducing pulmonary oedema to ease the associated clinical signs and make the patient more comfortable. Therapeutic procedures to drain effusions are also key in these cases to allow diuretic therapy to work.

Chronic CHF

In chronic CHF cases, the aim is to prevent recurrence of decompensation, control clinical signs and slow disease progression. Diuretic usage in these patients should be titrated carefully to each individual. This should be based on:

  • Sleeping respiratory rate (SRR) (see section 6).

  • Clinical picture: what clinical signs did the patient initially present with? Are these returning?

  • Quality of life: most importantly, how happy is the patient? Are they able to do the activities they enjoy the most? The aim of long-term treatment is to get them back to the activities that bring them, and their owners, happiness.

  • Compliance: make sure the owner is managing to give what you prescribed, otherwise long-term control will be impossible. Ask the owner at each recheck examination what medication they are giving and when.

3. What diuretics are available and what should I use?

Table 2 lists the diuretics that are currently available in the UK. Most vets are familiar with furosemide (frusemide): it has been the cornerstone of diuretic therapy for decades. Torasemide is a newer loop diuretic that has been gaining popularity in human medicine and has recently been licensed in veterinary medicine. Clinical trials have shown it to be as effective as furosemide in treating heart failure in small-breed dogs with mitral valve disease and there are potential benefits due to its increased duration of action, meaning less frequent dosing.

Table 2: Diuretics available to veterinary surgeons in the UK

Box 1 illustrates the management of a newly diagnosed case of CHF.

Box 1:

Case example

You have correctly diagnosed an eight-year-old Cavalier King Charles spaniel with degenerative mitral valve disease and congestive heart failure (CHF).

Diuretic therapy with furosemide (or equivalent torasemide dosing) for this patient will comprise the following:

  • Start at 2 mg/kg twice daily for two weeks, and then adjust this dose based on clinical response and sleeping respiratory rate (SRR).

  • If the SRR trend increases or goes above 30 breaths per minute consistently, increase to 3 mg/kg twice daily.

  • If SRR remains high or the patient has an acute episode of CHF, aim for 3 mg/kg three times daily for three to five days before starting to reduce as long as SRR is stable.

If the case appears refractory to diuretic, consider the potential reasons listed in Table 3. If these causes can be excluded then switch diuretic (eg, to torasemide from furosemide or vice versa). If you are still struggling to stabilise the patient, consider more than one diuretic (see Table 2).

4. Should I be worried about the adverse effects of diuretics?

Managing a patient on diuretics can be challenging. Diuretics will increase thirst and urination and although these signs usually improve within a week or two of starting, nocturia and urinary incontinence can become a serious side effect for owners.

Diuretics affect renal function and electrolyte balance, so checking these before starting therapy and periodically during treatment is important. Using the lowest effective dose is the best way to minimise adverse effects. The most common issue we see is misuse of diuretics in patients who are not in CHF, so avoiding this is the most important step.

5. My patient has concurrent disease, will this affect diuretic dose?

Patients most at risk of CHF (older, small-breed dogs) often have comorbidities. When diagnosing CHF, focus on looking for the following key comorbidities to make sure nothing is overlooked.

  • Renal disease: aiming for the lowest effective diuretic doses is more crucial in these cases. Patients with renal dysfunction need closer monitoring and may require rehydration with parenteral fluids at times.

  • Pulmonary hypertension is often confused with CHF, and might be why increasing doses of diuretic seem ineffective. This requires accurate diagnosis for treatment (see section 7 and Table 3).

  • Undiagnosed systemic hypertension may prompt higher diuretic doses as the left ventricle has to work harder, and fails more quickly. Equally, undiagnosed hypotension can complicate refractory cases, or may be present where over-diuresis has occurred. Getting into the habit of recording systolic blood pressure in CHF patients is a good idea.

  • Thyroidal illness: hypothyroidism in dogs can result in slower heart rates and reduced systolic function. In patients with CHF this limits the cardiac response and can worsen failure, making diuretic control more difficult. Cats with hyperthyroidism will conversely have faster heart rates, reducing filling time and thus decreasing cardiac output.

Table 3: Things to consider if a patient appears refractory to treatment for congestive heart failure (CHF)

6. How often do I need to check a patient on diuretics?

It is essential that owner expectation is managed correctly in any patient with cardiac disease, and those receiving diuretics generally need closer contact with their vet. Make sure you and the owner discuss how to manage the patient at home, including medication, change in toileting habits and the cost implications of drugs and rechecks. We largely rely on owners to judge the clinical changes in their animal, so educating them on what matters is key.

How often a patient is rechecked will vary between practices, but as a general guide we do the following.

  • Stable patients: ideally, stable patients are given a full assessment approximately every six months. If comorbidities (systemic hypertension/renal disease) are identified then we try to check every three months.

  • Unstable patients: it is important to stay in regular contact with unstable patients while you are trying to stabilise them. Try not to cause undue stress with repeat visits unless you are performing tests that will change your treatment plan. Telephone calls or emails are invaluable to assess SRR and clinical signs away from the clinic. Acute decompensation will need emergency intervention, but try to create a monitoring plan once the patient is safe to go home.

Always record an up-to-date weight. Dramatic changes might change dose efficacy, particularly in growing patients or those regaining lost weight.

Questions to ask the owner at rechecks

  • What is the SRR (Fig 5)? This is the most useful test for the presence of CHF as it gives us warning of increasing pressure in the pulmonary circulation causing pulmonary oedema. The patient MUST be sleeping but not dreaming. Demonstrate what constitutes a single breath and encourage the owner to document this, as it provides a key element to future monitoring. This should be monitored more frequently when doses have been changed. Online tools such as the Ceva ‘Cardalis’ app or Vetoquinol ‘UpLife’ site are free and very easy for clients to use.

  • What is the patient’s exercise tolerance? Are they still managing their usual walk or playtime at home? If not, how has this changed? Concurrent issues such as osteoarthritis or owner factors may affect this.

Fig 5: Monitoring the sleeping respiratory rate can give warning of increased pressure in the pulmonary circulation causing pulmonary oedema

In a destabilising patient, always go back to the original history taking (section 1). A change in home circumstances or concurrent diseases may be affecting diuretic management. Address these before proceeding with dose changes.

Which tests are useful?

  • Blood tests: assessing renal parameters and electrolytes for patients on diuretics enables early detection of azotaemia. If there is clinical suspicion of a comorbidity, investigate as appropriate (eg, thyroid function, haematology for anaemia, etc) as these will affect cardiac function.

  • Thoracic radiographs are useful not only in the diagnosis of CHF, but also where diuretic control is questioned. Radiographs just before the next diuretic dose may highlight active pulmonary oedema, indicating that an increased dose is needed. It is worth noting that patients with worsening cough due to cardiomegaly or pulmonary hypertension are often misdiagnosed as worsening CHF. If the SRR is normal, pulmonary oedema is highly unlikely.

7. How do I manage a refractory case?

One of the most common questions we get asked is how to manage a patient who is not responding to CHF treatment. We consider a patient with CHF refractory to diuretics if they are receiving more than 12 mg/kg/24 hrs furosemide alongside the appropriate pimobendan/spironolactone/angiotensin-converting enzyme inhibitor regime.

Although diuretic resistance is most often blamed as the cause, there are many things to consider when a patient appears refractory (Table 3).

Considering euthanasia where patient welfare is compromised is difficult, but potentially necessary.

8. Nursing a hospitalised patient in CHF

The role of veterinary nurses in caring for CHF patients can be easily overlooked. In human medicine, the introduction of dedicated heart failure nurses has been shown to improve clinical outcomes. If possible, enrol the vet nurses in your clinic to help manage your heart failure patients, both during hospitalisation and when at home. In a busy clinic it can be helpful for nurses to take on the responsibility of discussing home management with owners who will often have questions about care after their pet has been discharged.

The following aspects need to be considered when managing a hospitalised heart failure patient.

  • Medication: communication is key to make sure that everyone is aware of what diuretic dose, route and interval is expected. This should be recorded clearly.

  • Toilet breaks: dogs should be taken out more frequently (eg, hourly). Ascertaining which surfaces or substrates patients prefer (dogs: grass v tarmac, cats: litter type) on admittance can make a big difference.

  • Water provision: this is particularly important for all cases on diuretics and water bowls may need more regular refills.

  • SRR: monitor and clearly record the SRR to assess trends throughout the day and in association with medication.

  • Environment: noisy, stressful environments are deleterious. Locate patients where frequent monitoring is easy, and in close proximity to oxygen provision for patients who may have respiratory difficulty.

  • Diet: patients with cardiac cachexia may need slowly building up or those with concurrent renal disease may benefit from specific diets.

9. What about cats?

Cats present some peculiar challenges, but the same principles apply. Cats are much better at hiding signs of CHF, although clues about the likelihood of CHF can often be gained on a physical examination.


When treating cats, medication compliance – dose frequency, formulation and route of administration – should be taken into consideration.

  • In patients that are challenging to medicate, try to stick to only those medications that are essential and will make a clinical difference (such as diuretics).

  • As long as the patient is coping, add in other drugs – never start them all at once, as this commonly leads to medication aversion.

  • Reformulations in smaller doses such as such as clopidogrel (18.75 mg, Summit) and palatable furosemide tablets are easier in small patients. Liquid formulations are also an option (eg, Frusol [Rosemont Pharmaceuticals], a human furosemide solution; or clopidogrel oral suspension for cats [Bova]).


SRR is just as useful in cats as in dogs and should always be recommended to owners. Rechecking cats in CHF often causes much more stress, and vet trips should be managed with care (quieter times of day, cat-friendly clinics, or even home visits if possible).


The presentation of acute CHF in cats is most commonly in the form of respiratory distress. Before attempting tests to confirm, aim to:

  • Obtain a baseline heart rate, respiratory rate and temperature. These can be useful guides as to the cause of the respiratory distress (Dickson and others 2018).

  • Place the cat in an oxygen tent if possible (flow by oxygen if this is not available). Bear in mind that these can get warm inside so keep checking the patient.

  • If the patient is stressed, butorphanol (0.2 mg/kg intramuscularly) is useful to encourage slower, deeper breathing without heavy sedation.

  • If you can, TFAST scanning in the sternal position to assess left atrial size or the presence of pleural effusion is very useful to aid rapid treatment. Do NOT attempt full echocardiography or thoracic radiography until the patient is stable.

  • Give the first bolus of furosemide intramuscularly, as patients will often not tolerate an intravenous injection or catheter placement when stressed.

  • Thromboembolic presentations vary from hindlimb weakness and dragging the legs to being non-ambulatory. Make sure you assess femoral pulse quality and extremity temperature as this will guide your diagnosis.

10. Should I use a diuretic to help manage a pericardial effusion?

The short answer is ‘usually no’. If a patient presents with a pericardial effusion, it is important to know if tamponade is present. Tamponade is the clinical scenario when the pressure inside the pericardial space exceeds the intracardiac pressure. Typically, the right atrium has the lowest pressure and so when tamponade occurs, the right atrium collapses and is unable to fill (Fig 6). This causes right heart failure (ascites, pleural effusion).

Fig 6: Tamponade. Note the collapsed right atrium (RA) in the presence of a pericardial effusion (PE). RV Right ventricle, LV Left ventricle

A common mistake with a patient in tamponade is to give diuretics to reduce the fluid accumulation, but this actually makes the patient worse by reducing circulating volume and lowering the pressure in the right atrium further, making the tamponade worse.

If tamponade is present, the key treatment is pericardiocentesis to reduce the extracardiac pressure, sometimes with supportive intravenous fluids to maintain cardiac filling. So in most patients with pericardial effusion, tamponade and signs of right heart failure, diuretics should be avoided until the tamponade is relieved by pericardiocentesis.

Summary: the take-home messages

  • Make the correct diagnosis.

  • SRR is key to assessing the development of cardiac disease.

  • When treatment is not working, go back to basics.

References and further reading

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