A venous cannula apparatus is comprised of a fluid conveying tube, the tube providing an upper tube portion which communicates with a pair of lower connected tube branch members. Each of the lower tube branches is normally in an angular position with respect to the upper tube, thus allowing the tube branches to coincide with the atrium, superior vena cava and inferior vena cava during an operation requiring a cardio pulmonary bypass. In the preferred embodiment, two flexible lower branch members are provided forming a "wye" or "tee" with the upper tube portion. The entire cannula structure is manufactured of a material having a "memory" so that after a flexure of the branch members, they return to their operative or normal "tee" or "wye" position. A substantially stiffened sleeve member is cooperatively associated with and connectable to the fluid conveying tube, the sleeve being slideable about the tube and being capable of urging the lower tube branches into an aligned position with the upper tube portion. The apparatus can be utilized during a cardiopulmonary bypass, with only a single opening being formed in the atrium. The cannula apparatus is operatively inserted through an opening surgically formed in the atrium. Removal thereafter of the sleeve allows the branch members to diverge and insert respectfully into the superior and inferior vena cava. Closures form substantially fluid tight seals between the cannula structure and the heart before bypass begins.