Pulmonary artery balloon counterpulsation was instituted in 10 pigs when right ventricular failure limited cardiac output. Global myocardial depression was produced by infusion of propranolol, and the left ventricle was fully supported by left heart bypass. A stable model of failure was achieved in six pigs. Following application of pulmonary artery balloon counterpulsation right atrial pressure decreased from 18.2 +/- 2.1 to 15.9 +/- 2.5 mm Hg (p less than 0.05). Cardiac output increased from 416 +/- 94 to 758 +/- 127 ml/min (p less than 0.001). Right ventricular stroke work increased from 0.29 +/- 0.07 to 0.65 +/- 0.12 gm X m. (p less than 0.05). There was no cardiac output before or after institution of balloon counterpulsation in four pigs studied during ventricular fibrillation or asystole. We conclude that pulmonary artery balloon counterpulsation improved cardiac output and right ventricular stroke work in a model of right ventricular failure where the pulmonary circulation was unaltered and the left ventricle supported by left heart bypass. Balloon counterpulsation was not effective during ventricular fibrillation or asystole. Pulmonary artery balloon counterpulsation should be considered when right ventricular failure limits cardiac output during left heart bypass.