Isosorbide mononitrate in a dose of 20 mg t.i.d. was used in 25 patients admitted few hours after acute myocardial infarction. The following parameters were analysed: systolic and diastolic blood pressure, heart rate, clinical features, and laboratory data. Heart rate and diastolic blood pressure remained unchanged, however systolic blood pressure was slightly reduced (p less than 0.01). There was a reduction in the angina episodes post-AMI. None of the patients included in the study had clinical deterioration or showed infarction extension. There were no changes in laboratory data. After the interruption of the drug, one patient died on the 6th day with acute mitral insufficiency. In conclusion, isosorbide mononitrate can be safely used during an uncomplicated acute myocardial infarction, without the risk of haemodynamic deterioration, and helps to prevent post-infarction angina.