In the course of the routine evaluation of a 26-years-old male for acquired aortic valve disease the persistence of a left superior vena cava draining into the coronary sinus was detected. This is a frequent congenital malformation of the systemic venous system that has no hemodynamic consequences in itself, though it may be associated to other congenital or acquired cardiac malformations that may require surgery. The preoperatory detection of the anomaly prevents unexpected problems when connecting the cardiopulmonary bypass. We emphasize the importance of procedures that suggest the diagnosis and characterize the anatomo-functional nature of the condition--including transthoracic and transesophageal echocardiography using echocardiographic contrast, and cardiac catheterization with cardiac and vascular angiography.