The efficacy of pulmonary artery balloon counterpulsation (PABC) was evaluated in improving right ventricular (RV) output during left heart bypass for global cardiac failure. In 13 pigs, a 40-ml balloon was positioned within a graft anastomosed to the pulmonary artery distal to the pulmonary valve, and left heart bypass was instituted from the left atrium to the carotid artery. Global myocardial failure was produced by an infusion of propranolol (range, 25 to 78 mg). In this model, RV output decreased despite volume loading to a right atrial pressure of 15 mm Hg and atrioventricular sequential pacing at 100 beats per minute. Pulmonary artery balloon counterpulsation increased both RV output (from 519 +/- 76 to 1,117 +/- 110 ml/min; p less than 0.01) and RV systolic stroke work (from 1.3 +/- 0.4 to 2.3 +/- 0.6 gm-m; p less than 0.01). Right atrial pressure decreased (from 15.5 +/- 0.9 to 10.7 +/- 1.0 mm Hg; p less than 0.01) in 8 of the pigs studied during RV failure. In 5 pigs, ventricular fibrillation occurred without a stable model of RV failure, and there was no cardiac output before or after counterpulsation. The mechanism of action of PABC was studied by placing a flow probe around a large branch of the right pulmonary artery. During RV failure, balloon inflation caused flow through the pulmonary circulation, and ventricular systole resulted in filling of the graft. During ventricular fibrillation, balloon inflation and deflation produced only a to-and-fro movement of blood in the pulmonary artery branch without net forward flow.(ABSTRACT TRUNCATED AT 250 WORDS)