For the in vivo evaluation of a pulsatile impeller total heart, biventricular assistance was performed in five pigs weighing 30-50 kg. The left pump delivered blood from the left atrium to the aorta, and the right pump from the right atrium to the pulmonary artery. The bypass flow on both sides was adjusted to about 40-50% of the total flow. Hematologic variables were measured every 2 hr during the 6 hr experiments. Results demonstrated that the pulsatile impeller total artificial heart causes no blood damage and can be used in chronic survival experiments.