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Cardiovascular Collapse
Mike Martin MVB DVC MRCVS (RCVS Recognised Specialist in Veterinary Cardiology)

Collapsing dogs are a common reason for referral. Dogs can have symptoms present at the time of examination or not. If they have symptoms or clues from diagnostic tests at the time of examination, then a diagnosis is relatively easy. Whereas, if they present with no symptoms or clues at the time of examination, then the diagnostic rate falls to as little as 50%.

A large amount of information must be gathered at the initial consultation with the owner. Without a very thorough history, it is difficult to reach a diagnosis of syncope versus neurological or other causes of collapse. It is essential to know what the dog’s activity level was at the time of collapse. Most often cardiovascular syncope occurs on excitement or exertion. If recurrent, signs often occur under similar conditions on each occasion. The earliest clinical signs noticed by the owner are important. With syncope there is usually abrupt collapse into lateral recumbency or a brief phase of unsteadiness (ataxia) before the collapse.

It is essential to know what the dog's activity level was at the time of collapse
The dog may or may not be responsive during the collapse. Urination is quite common during syncope. If syncope is prolonged, stiffness of the limbs or even opisthotonus could follow but the collapse will be ‘limp’ initially before these signs eventually occur. Such signs are rare however - the majority of syncopal dogs remain limp. Pallor of the gums is common but not inevitable. Recovery is usually brief with a rapid return to normality. However sometimes dogs are lethargic or ‘washed out’ for several hours after the event.

Approach to Suspected Syncope

A video recording by the owner of a collapsing event may be very useful if available, as the actual syncope is rarely witnessed by the veterinarian. Observation of mucosal colour during collapse is also useful.

Clinical examination with particular emphasis on a prolonged auscultation for arrhythmias (these may be intermittent, however) and also to detect murmurs on either left or right side is advised. In addition both femoral pulses and degree of jugular distension should be assessed.

Echocardiography is useful in most cases of suspected syncope. It is most helpful if there is a history of exercise intolerance or in the presence of a  prominent murmur or arrhythmias; also in breeds predisposed to syncope or heart disease (Boxer, Doberman, giant breeds).

A full blood profile with T4/ TSH and potentially also bile acid stimulation & ACTH tests are advised if there are systemic problems identified, e.g. weight loss, anaemia, reduced appetite.

Blood pressure assessment is useful in all cases, especially if they present with symptoms at the time of examination.

If an arrhythmia is present, a standard ECG recording is likely to be informative. However if none is apparent on auscultation, a resting ECG is debatable. In such cases, or where syncope is quite intermittent, prolonged Holter ECG recording is likely to be beneficial. Holters can record over 4-5 days if necessary. Even if the dog does not collapse while Holtered, useful information is often gained during the recording. For example, significant periods of bradycardia/ asystole or tachycardia may be recorded on Holtering in the absence of any noticed clinical signs by the owner. 

In some dogs, even after an extensive work up there may be no abnormalities identified. In these dogs a neurological work up may be warranted. Seizures are much more likely to occur at rest than at exercise, in contrast to syncope. Muscular disease can lead to an altered gait or stride pattern, or to muscular stiffness, on exertion. Neuromuscular disease often leads to sitting down/ collapse of the hind legs without syncope. Pallor is not expected during collapse due to muscular or neuromuscular diseases.

Examples of collapsing dogs referred to us recently:
  • Cocker spaniel - DCM
  • Bull terrier - Mitral stenosis and aortic stenosis   
  • Boxer - Vasovagal syncope
  • Collie cross - Intracardiac mass
  • Boxer - Ventricular tachycardia
  • Boxer - Subaortic stenosis
  • Cross breed - Third degree AV block
  • Boxer - Subaortic stenosis
  • Cocker spaniel - DCM
  • Labrador - Atrial mass
  • Labrador - Mitral and tricuspid endocardiosis
  • West Highland white terrier - Sick sinus syndrome
  • Labrador - Third degree AV block
  • Boxer - Subaortic stenosis
  • St Bernard - DCM  

Case Example One

A 4 year old male Labrador was referred for the investigation of multiple episodes of collapse over a one year period. Initially the events were infrequent but had increased to up to six collapses daily, at rest or at exercise. Each collapse was very brief, lasting only seconds before making a full recovery. His exercise tolerance had decreased noticeably for six months. 

He was diagnosed with bradycardia due to third degree AV block and a pacemaker was fitted. No further collapses have occurred to date.

Case Example Two

A 7 year old female Cocker spaniel presented with a history of one recent collapsing event. On excitement, she fell into lateral recumbency and appeared limp for 30 seconds. She urinated during the collapse. Recovery was very rapid with no after effects. Mild exercise intolerance had been noted for one to two months.

DCM was diagnosed and therapy with heart medications and taurine started. No further collapses have occurred three months later.


Text and photographs by Mike Martin, of Martin Referrals; we would like to thank Mike for granting us permission to publish his article.

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WellVet launches spring series of wellbeing talks

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 A new spring series of wellbeing talks designed to tackle some of the issues faced in veterinary practices is launching on Saturday (27 February). Hosted by WellVet and Boehringer Ingelheim, the talks will focus on simple, practical tips to improve personal and team wellbeing.

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