The effect of 0.3 mg sublingual nitroglycerin (NTG) was evaluated by hemodynamic measurements and precordial S-T-segment mapping in 17 patients following acute myocardial infarction.In all cases NTG produced a prompt reduction in mean pulmonary capillary wedge pressure (PCW) from an average of 19 ± 2 to 14 ± 1 mm Hg associated with a small fall in mean arterial pressure from a mean of 85 ± 4 to 82 ± 4 mm Hg. No significant change in heart rate occurred.In patients without left ventricular failure (PCW 3-12 mm Hg) cardiac output (CO) fell 9%. By contrast, in patients with moderate left ventricular failure (PCW 13-22 mm Hg) CO rose 18%. In three patients with refractory left ventricular failure (PCW 25-31 mm Hg) CO rose 25%. Two of these patients were treated with repetitive NTG doses in addition to previously ineffective diuretic therapy with resolution of resistant pulmonary edema. No significant changes in the magnitude of S-T-segment elevations were noted.NTG may have a special role in the management of acutely ill patients with myocardial infarction in whom pulmonary edema does not respond to conventional therapy.