Aortic endocarditis in a dog with subaortic stenosis
4-year-old Boxer with known moderate subaortic stenosis. For a week it has had fever (40.1 °C), lethargy and shifting lameness. Besides the usual systolic murmur, you now hear a diastolic murmur at the left base and the pulses are bounding. Echocardiography shows an oscillating lesion on the aortic valve.
What is the most appropriate next step?
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A. Immunosuppressive prednisolone for immune-mediated polyarthritis
Polyarthritis can accompany endocarditis (immune complexes or septic emboli). Immunosuppressing a dog with an active valvular infection is dangerous.
B. Oral amoxicillin and a recheck in two weeks
Endocarditis needs bactericidal antibiotics, initially intravenous and for weeks to months, chosen after blood cultures. A short empirical oral course is insufficient and makes cultures negative.
C. Wait for blood culture results before giving any antibiotic
Aortic endocarditis destroys the valve rapidly and may cause heart failure and emboli. Once samples are taken, empirical treatment must start immediately and be adjusted later according to culture.
D. Collect several blood cultures from different sites and immediately afterwards start broad-spectrum intravenous bactericidal antibiotics
Correct. Fever, a new diastolic murmur of aortic regurgitation and a valvular vegetation indicate infective endocarditis. Take 2–3 aseptic blood cultures from different veins before antibiotics and do not delay empirical treatment while waiting for results.
lightbulb Key takeaway
Subaortic stenosis is the clearest cardiac risk factor for aortic endocarditis in dogs, because the turbulent jet damages the valve endothelium. A new diastolic murmur in a febrile dog is endocarditis until proven otherwise. If blood cultures are negative, think of Bartonella. The prognosis of aortic endocarditis is guarded.
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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.