Molsidomine, a new long-acting vasodilator, was administered intravenously (0.03 mg per kilogram of body weight) to two groups of six patients with stable anginapectoris. In the first group, studied during exercise-induced angina, the drug shortened the duration of pain and reduced electrocardiographically measured ST-segment depression, mean systemic arterial pressure, and mean pulmonary wedge pressure. Cardiac output and heart rate remained unchanged. In the second group, studied during pacing-induced angina, the drug reduced both left ventricular pressures and angiographically estimated ventricular volumes and improved the ejection fraction. In a double-blind crossover comparison with a placebo, molsidomine (2 mg three times daily) reduced the frequency of anginal attacks and the consumption of nitroglycerin tablets in 14 patients. During exercise testing on a treadmill a statistically significant reduction in ST-segment depression lasted for up to six hours. These studies suggest that molsidomine acts like nitroglycerin but its effects last longer. We conclude that molsidomine is effective in preventing the symptoms of angina pectoris. (N Engl J Med 302:1-6, 1980).