Common ventricle is a rare congenital anomaly in which the ventricular chamber receives blood from two separate atrioventricular valves or from a common atrioventricular valve. We used contrast echocardiography during cardiac catheterization to confirm ventricular anatomy and to characterize blood flow dynamics in 35 patients with common ventricle. After injections of dye, a cloud of echoes anterior to the mitral valve echo during the rapid inflow phase of ventricular diastole is indirect evidence of common ventricle with two atrioventricular valves. Common ventricle with an outflow chamber is characterized by a smaller ventricular chamber visualized anterior to both atrioventricular valves which opacifies with subsequent ventricular systole. The arrival of all dye posterior to the only recorded atrioventricular valve further established the presence of a single atrioventricular valve. These contrast flow patterns gave greater specificity to the standard M-mode echocardiographic assessment of patients suspected of having common ventricle.