Experiments were undertaken to examine whether and how intravenous infusion of ISDN ameliorated hemodynamics of anesthetized dogs with congestive heart failure. A model of acute congestive heart failure with markedly high left ventricular end-diastolic pressure (LVEDP) and low cardiac index (CI) was induced by occlusion of the left anterior descending coronary artery (LAD) following 30-min infusion of dextran solution containing propranolol in halothane anesthetized open-chest dogs. Five minutes after occlusion of LAD, intravenous infusion of ISDN (100 and 500 micrograms/kg/min for 5 min) decreased the elevated LVEDP, aortic pressure and systemic vascular resistance, and enhanced the reduced CI. These changes produced by ISDN were significant (P less than 0.05 or P less than 0.01) as compared with values just before infusion of ISDN. ISDN at the same doses slightly reduced LVEDP, but did not increase CI in normal dogs which were not subjected to the coronary occlusion and dextran infusion. These results indicate that intravenous infusion of ISDN reduces both pre- and after-load and increases CI in dogs with heart failure, demonstrating that ISDN is useful for the vasodilator therapy of heart failure.