Heart base mass in dogs: chemodectoma
10-year-old Boxer with exercise intolerance. Echocardiography shows a 4 cm homogeneous mass at the heart base, adjacent to the ascending aorta and pulmonary artery, with mild pericardial effusion. The right atrium and auricle are normal.
What is the most likely diagnosis?
chevron_right Show answer and explanation
A. Haemangiosarcoma
It is the most common cardiac tumour in dogs, but it usually arises in the right atrium or auricle, which are normal here.
B. Mesothelioma
Mesothelioma diffusely affects the pericardium and usually causes recurrent effusion without a discrete mass. It is hard to distinguish from idiopathic pericarditis.
C. Chemodectoma (aortic body tumour)
Correct. It is the typical heart base tumour, with a predisposition in brachycephalic breeds (Boxer, Bulldog), possibly due to chronic hypoxia. It grows slowly and metastasises late.
D. Cardiac lymphoma
Cardiac lymphoma is more common in cats; in dogs it usually infiltrates the myocardium or pericardium diffusely and is accompanied by multicentric disease.
lightbulb Key takeaway
Location on echocardiography is the best clue to the type of cardiac tumour. In chemodectoma with pericardial effusion, pericardiectomy can greatly prolong survival because the tumour progresses slowly.
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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.