[A 34-year-old male presented with fatigue, weight loss, double vision and extra heart sounds].

BACKGROUND: The diagnosis of culture-negative endocarditis, defined as an active infection of the endocardium in the absence of positive blood cultures, is challenging. MATERIAL AND METHODS: A 34-year-old male presented with persistent fever and negative blood cultures. The echocardiogram showed a bicuspid aortic valve, severe aortic regurgitation, an abscess cavity in the aortic root, and a mass on the anterior leaflet of the mitral valve. The abscess cavity could be visualised only with transoesophageal echocardiography. RESULTS: The diagnosis of infective endocarditis could be established clinically with the Duke criteria. The echocardiographic findings were confirmed at surgery. Cultures of the excised tissue were negative, but histology showed strong evidence of infection. INTERPRETATION: The Duke criteria can be useful in the assessment of a clinical diagnosis in subjects with endocarditis and negative blood cultures. Transoesophageal echocardiography is especially important in this setting.