Intravenous nitroglycerin (IV-NTG) has gained wide use in the manage ment of critically ill patients, yet little is known regarding dose-response hemodynamics in man. Therefore, we studied 10 patients, all Class III or IV New York Heart Association Classification with pulmonary artery wedge pressures of 15 torr or greater. A special delivery system designed to prevent drug absorption Nitrostat® IV Infusion Kit was used and assessed. Multiple hemodynamic values were recorded before, during, and after the infusion. Administration of IV-NTG was started at 0.125 mcg/kg/min and was doubled every 15 minutes to a maximum dose of 2.0 mcg/kg/min. The infusion was stopped if the pulmonary artery wedge pressure dropped below 10 torr, or arterial pressure dropped below 90/60 torr, or if the mean artery pressure fell more than 10 torr, or if significant side effects occurred. Samples for blood levels were collected. Only one patient noted any untoward effects and he recovered quickly upon cessation of infusion. The mean infusion rate was 0.6125 mcg/kg/min. A significant drop in mean arterial blood pressure, mean pulmonary artery pressure, mean pulmonary artery wedge pressure, heart rate, and arterial oxygenation was noted. Cardiac output did not change significantly. Pulmonary vascular resistance index, as well as several other indices, decreased significantly in all patients. Nitrostat IV® appears to be very safe and to work by dilating preload capacitance vessels, followed by a drop in arterial pressure without an adverse lowering of cardiac output.