A 75-year-old asymptomatic male patient was referred for transesophageal echocardiography after detection of a diastolic murmur on routine physical examination and widened mediastinum on a chest radiograph. Transesophageal echocardiography revealed a large, unruptured sinus of Valsalva aneurysm, filled with a thrombus and spontaneous echocontrast and protruding into the right atrium. Unruptured sinus of Valsalva aneurysms are rare, frequently asymptomatic, and not associated with any physical findings. The diagnosis was made by transesophageal echocardiography and was confirmed by angiography and at surgery. The need for corrective surgery of asymptomatic, incidentally diagnosed sinus of Valsalva aneurysm is not well defined in the absence of precise knowledge of its natural history. We provide a description of the natural history and rationale for early corrective surgery of sinus of Valsalva aneurysms in asymptomatic patients.