Clinical, instrumental and post-mortem studies were carried out in a patient with intractable cardiac failure, whose death was attribute to Weil's syndrome. A post-mortem examination showed the presence of numerous petechiae on the heart layers and diffuse lymphomonocytic infiltrates in the myocardium, epicardium and endocardium. We suggest that in patients affected by leptospirosis--an endemic disease with a possible fatal outcome--it is necessary to determine carefully any involvement of the cardiovascular system which may play a determinant role in the evolution of the disease.