Venting of the Heart : It is important that heart does not distend during cardio pulmonary bypass. This is prevented by venting of the left side of the heart by inserting a cannula into the left atrium, left ventricle, pulmonary artery or aortic root below the cross clamp. The cannula is connected to low suction and the same cannula is used for &airing of the chambers of the left heart at the end of the intracardiac procedure.