Left atrial rupture in MMVD: haemopericardium
13-year-old Poodle with severe MMVD and a markedly dilated left atrium that collapses suddenly. Pale mucous membranes, weak pulse, tachycardia. Echocardiography: moderate pericardial effusion with echogenic material consistent with a clot, diastolic right atrial collapse and no visible mass.
What is the most likely diagnosis?
chevron_right Show answer and explanation
A. Right auricular haemangiosarcoma
It is the most common cause of haemopericardium in large-breed dogs (German Shepherds, Golden Retrievers). In a Poodle with severe MMVD and no visible mass, atrial rupture is more likely.
B. Tear of the left atrial wall with haemopericardium and tamponade
Correct. The high-velocity regurgitant jet damages the endocardium of the markedly dilated left atrium and may eventually tear the wall. Blood in the pericardium causes acute tamponade; the clot and absence of a mass in a dog with severe MMVD support the diagnosis.
C. Idiopathic pericarditis
It is typical of medium-to-large breeds (Golden Retrievers) and causes recurrent effusions of more gradual onset, not sudden collapse with a clot in a dog with end-stage MMVD.
D. Rupture of a mitral chorda tendinea
Chordal rupture causes acute massive regurgitation and fulminant pulmonary oedema (sometimes with a flail leaflet on echocardiography), but not pericardial effusion.
lightbulb Key takeaway
In tamponade from atrial rupture, pericardiocentesis is reserved for haemodynamic instability and only what is necessary is removed, as the pericardial clot may be sealing the tear. Avoid diuretics while tamponade persists. Prognosis is guarded, although some dogs survive if the bleeding is self-limiting.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.