The efficacy of isosorbide dinitrate (ISDN) and nitroglycerin was studied in 115 patients with acute transmural myocardial infarction admitted to the Coronary Care Unit not later than 12 h after the onset of chest pain: 58 patients not later than 2 h after the onset of chest pain, 49 after 3–6 h and 8 patients in the period of 6–9 h. There were 69 men and 45 women, mean age 62.4 ± 0.9 years. The duration of the preceding clinically evident coronary artery disease was in 12 patients 1 year, in 29 2–3, in 22 4–5 and in 16 patients 6 years or more. In 36 cases the chest pain of acute infarction was the first presentation of coronary artery disease. Thirty-seven patients had a previous myocardial infarction. Fifty patients had concomitant systemic hypertension. The patients were divided into 3 groups depending on the type of therapy received: group I, receiving anticoagulants only, served as control; patients of groups II and III received, in addition to the anticoagulants, intravenous ISDN or nitroglycerin, respectively. The patients were monitored for recurrent chest pain, electrocardiographic changes, clinical parameters and cardiac enzyme changes. ISDN, at a dose of 10 mg/h over the first 3 days of infarction, had marked antianginal effect, limited the dimensions of the necrotic area, reduced the number of ischemic relapses and the development of heart failure. Compared to nitroglycerin, ISDN exerted a more prolonged action (up to 12 h), did not affect heart rate and blood pressure, and had a marked antiarrhythmic effect. This last finding widens the indications for the use of ISDN in patients with myocardial infarction.