Univentricular heart or common ventricle can be defined as a heart that has a ventricular chamber that recieves both antrioventricular valves or one atrioventricular valve. Hallermann's angiographic modification of Van Praahg's classification is a practical and useful classification of this complex abnormality. The classification divides univentricular heart into two types namely type A, those with an outflow chamber and type C, those with an outflow chamber. The relative position of the great arteries further subdivides the types of common ventricle. Thus, common ventricles may have a normal relative relationship of the great arteries but more frequently the great arteries are transposed in a levo or a dextro position. The most common type of common ventricle in the type A-3. A review of 145 cases of common ventricle seen at the Mayo Clinic comprises the majority of this report. Age range in this series is from seven days to 38 years with a mean age of 8.4 years. Males are slightly more dominent than females roughly in a ratio of 2:1. Type A common ventricle occurred in 63 percent of the cases and tye C occurred in 37 percent of the cases. Simultaneous saturations from the pulmonary arteries and femoral arteries in this show that complete mixing occurs in approximatley 50 percent of these cases but in the other 50 percent of the cases great differences may be seen and are not related to the great vessel position. Obstruction at the bulboventricular foramen while it can be severe is usually not. M-mode echocardiography has been of great help in the diagnoisis of common ventricle and features are listed. Two dimensional real time sector echocardiography; however, forms a much more detailed diagnosis and many times showed details particularly in valvular anatomy that is not seen by conventional angiocardiographic techniques. Attention to the detail of preoperative diagnosis from a hemodynamic and anatomic standpoint will avoid many errors usually discovered at the time of surgery.