Hemodynamic effects of vasodilator agents (molsidomine, nitroglycerin, isosorbide dinitrate or prostaglandin I2) were studied in 53 patients with acute myocardial infarction. In 20 of these patients, effect on cardiac metabolism were also studied. Patients were divided into four groups according to the Forrester subset and hemodynamic effects of these agents were evaluated by the cardiac index (CI)-preload (PAEDP) relationship. In patients of Forrester subset II and IV, vasodilators were capable of producing a considerable reduction in preload without a significant decrease in cardiac output. However, in patients of Forrester subset IV, five of six patients had only a minimal improvement in cardiac performance with vasodilator therapy because of a severe pump failure. In these patients, a combination therapy with dopamine was necessary to maintain the cardiac output. In patients with Forrester subset III, vasodilator therapy decreased cardiac index and preload was also reduced. Thus, for these patients vasodilators could not be indicated but volume infusion may be indicated. In patients with Forrester subset I, although vasodilator therapy decreased cardiac output, coronary sinus flow and myocardial oxygen consumption were also decreased, indicating that the vasodilator therapy is also beneficial for patients even without heart failure because of the protective effect of unloading on ischemic myocardium. Three nitrate agents, i.e., molsidomine, nitroglycerin and isosorbide dinitrate, demonstrated the similar effect on hemodynamics; mean blood pressure and PAEDP decreased by 7-10% and 20-29%, respectively, while systemic vascular resistance was not significantly decreased. In contrast to nitrates, PGI2 decreased mean blood pressure and systemic vascular resistance significantly, whereas a decrease in PAEDP was minimal.(ABSTRACT TRUNCATED AT 250 WORDS)