Profound right ventricular failure was produced in 16 goats by inducing ventricular fibrillation after the systemic circulation had been supported with a left atrial-aortic bypass pump. In each animal, four methods of providing pulmonary blood flow were compared quantitatively: passive flow through the pulmonary artery due to a right atrial to left atrial pressure gradient; pulmonary artery pulsation via a 40 ml intra-aortic type balloon within a 20 mm Dacron graft anastomosed to the main pulmonary artery; pulmonary artery pulsation via a 65 ml single-port, valveless, sac type pulsatile assist device; and right atrial-pulmonary arterial bypass via a valved pneumatic pulsatile pump. Average cardiac index of the 16 animals for each method was 31.1 +/- 12.9, 44.4 +/- 13.6, 64.3 +/- 16.9, and 102.0 +/- 20.7 ml/min/kg, respectively. Passive pulmonary artery flow alone provided inadequate pulmonary circulatory support. Addition of pulmonary artery pulsation via the intra-aortic balloon within a conduit increased cardiac index 13.3 ml/min/kg (43%) above passive pulmonary artery flow (p less than 0.0005); however, the cardiac index remained inadequate. Increasing pulmonary artery pulsation volume with a 65 ml sac device provided a 32.2 ml/min/kg (106%) increase in cardiac index above passive flow (p less than 0.0005) to a level that was marginally adequate. The valved right atrial-pulmonary arterial bypass pump increased cardiac index 70.9 ml/min/kg (228%) above passive pulmonary artery flow (p less than 0.0005) to a satisfactory level and is the recommended method of pulmonary circulatory support in profound right ventricular failure.