The Patient with Cardiac Tamponade
26th October 2026
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Cardiac compression – get the facts, act fast
Pericardial effusion with cardiac tamponade is a potentially life-threatening emergency that can be missed. A collapsed, tachycardic patient with poor pulses and ascites can trick you into reaching for diuretics, which will only make things worse. So, how do we recognise these patients, identify the problem quickly and decide what needs to happen next?
Our cardiology team is always happy to discuss your case or arrange a referral.
The pericardium is the sac surrounding the heart. When fluid accumulates within this space, pressure builds around the heart and restricts its ability to fill during diastole.
When this pressure becomes sufficient to impair cardiac filling and reduce cardiac output, the result is cardiac tamponade. Less blood returns to the heart, less blood is pumped around the body, and tissue perfusion deteriorates. The patient can develops signs of shock.
The severity depends not just on the volume of fluid, but also on how quickly it accumulates. Patients with an abnormal pericardium (restrictive pericarditis) also need very little fluid to cause a problem. A relatively small volume of rapidly accumulating fluid can cause severe compromise, whereas a slower accumulation may be better tolerated for longer, as there is some ability for the pericardium to stretch.
The presentation can be vague initially, although some can be normal one minute and collapsed the next. Common findings include:
Some patients present primarily with abdominal enlargement or recurrent ascites rather than obvious respiratory signs. This reflects impaired right-sided filling and increased systemic venous pressure.
Importantly, the absence of crackles doesn’t rule out a serious cardiac emergency. Unlike typical left-sided congestive heart failure, cardiac tamponade primarily impairs cardiac filling rather than causing pulmonary oedema.
The aim is to identify the effusion, establish whether it is causing tamponade, and assess how compromised the patient is.
If available, focused thoracic focussed (TFAST) ultrasound is an excellent first step in an unstable patient. It can rapidly identify pericardial fluid and help distinguish it from pleural effusion.
Echocardiography is the preferred diagnostic investigation. It can confirm pericardial effusion, assess its haemodynamic significance and identify signs of cardiac chamber collapse, particularly the right atrium and right ventricle. A more complete examination may also reveal an underlying cardiac mass. If the patient is not unstable, visualisation of some cardiac structures is slightly easier with fluid present, but the patient should not be compromised to await echocardiography.
Not to be prioritised in acute, unstable patients. A large, rounded or globoid cardiac silhouette can support the diagnosis, particularly in more chronic effusions. However, radiographs may be unremarkable in acute haemorrhage, so a normal-looking cardiac silhouette doesn’t exclude the condition.
Sinus tachycardia is common. Low-voltage QRS complexes and electrical alternans (alternating QRS amplitude as the heart moves within the fluid-filled pericardial sac) may also occur, but their absence doesn’t rule out an effusion or tamponade – it helps to support the diagnosis if present with other findings.
Blood pressure, pulse quality, mucous membrane colour, capillary refill time, mentation and lactate can help assess the severity of circulatory compromise and monitor response to treatment. These findings should be interpreted alongside imaging and the overall clinical picture.
If cardiac tamponade is causing haemodynamic compromise, the priority is to relieve the pressure around the heart.
Pericardiocentesis is the definitive emergency treatment. Removing fluid from the pericardial space allows the heart to fill more effectively and can rapidly improve cardiac output.
Depending on the patient’s condition and available facilities, immediate priorities include:
If the patient is unstable and your practice cannot safely perform pericardiocentesis, contact an emergency or referral centre immediately. Discuss the patient’s stability and whether drainage is needed before transport. Do not delay definitive treatment while pursuing non-essential diagnostics.
Take the pressure off the patient (and yourself): the aim here is not to remove every last drop of pericardial fluid to make any difference. Ideally, pericardiocentesis would take the majority of fluid away (and allow sampling for assessment), but even just puncturing the pericardium will allow release of some fluid into the thorax and immediately take the pressure off the heart. Sometimes, this can make the difference between life and death if the patient is too unstable to travel.
This is worth emphasising because cardiac tamponade can resemble right-sided congestive heart failure, particularly when ascites is present. However, the underlying problem is different. In congestive heart failure, diuretics may be essential to reduce fluid accumulation. In cardiac tamponade, the heart is being compressed externally and cannot fill properly.
Diuretics reduce circulating blood volume and venous filling pressures and are contraindicated in acute cardiac tamponade. In a patient whose cardiac output is already compromised by tamponade, this can further reduce cardiac filling, worsen hypotension and signs of shock. Likewise, don’t assume that a large abdomen means the patient needs diuresis. Establish the cause of the ascites before treating it as congestive heart failure.
Due to reduced diastolic capabilities in tamponade, the heart may also appear to have reduced systolic function, particularly when tachycardic (less time in diastole). While pimobendan might seem like the right drug to reach for to improve contractility, it does not target the underlying issue of tamponade. It is important not to increase myocardial workload even further, where possible. After pericardiocentesis following tamponade, cardiac function rapidly begins to improve. The heart can look a little ‘stunned’ in the immediate post-pericardiocentesis period, so cardiologist assessment is recommended to see if there is truly a systolic dysfunction present in the patient.
Draining the pericardium treats the immediate problem, but identifying the underlying cause is essential for further management and prognosis.
In dogs, the main considerations include:
Following stabilisation, a more complete echocardiographic examination should assess the right atrium and auricle, heart base and other visible cardiac structures for masses. Abdominal ultrasound is also worth considering, particularly to assess the spleen and liver for masses or other abnormalities that could influence the investigation and management plan.
Finding a mass doesn’t automatically establish its nature, and not finding one doesn’t exclude neoplasia. Some lesions can be difficult to visualise, so further investigation and specialist assessment may be appropriate.
Fluid analysis may help in selected cases, but haemorrhagic pericardial fluid alone rarely distinguishes neoplastic from idiopathic disease reliably.
Cats can also develop pericardial effusion, but the underlying causes and clinical context differ, with congestive heart failure and other systemic disease important considerations.
Early discussion with a cardiologist is valuable when pericardial effusion is identified, particularly if tamponade is present, a mass is suspected, or the effusion recurs following drainage. Specialist input can help with echocardiographic assessment, investigation of the underlying cause, decisions about repeat drainage or surgical management, and discussion of prognosis.
Recurrent effusion may require further intervention, including a pericardiectomy in selected patients. The most appropriate approach depends on the suspected cause, recurrence pattern and the patient’s overall condition.
Pericardial effusion and cardiac tamponade can present with vague signs, including weakness, collapse and ascites, but the consequences can be rapidly life-threatening.
Remember the key distinction: tamponade prevents the heart from filling. Recognise the signs of obstructive shock, use ultrasound to look for pericardial fluid where available, and prioritise urgent drainage when tamponade is compromising circulation.
And perhaps most importantly, don’t let the distended abdomen fool you into reaching for diuretics. In these patients, relieving the pressure around the heart (rather than reducing circulating blood volume) is what can make the difference.
Cardiac compression – get the facts, act fast
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