The aim of this article is to assess the therapeutic value of standard heparin in the acute phase and secondary prevention of myocardial infarction. Only clinical trials with an adequate methodology have been analysed. In patients having undergone thrombolytic therapy associated with aspirin, heparin slightly reduces the mortality but only during the period of its administration. In a metaanalysis of approximately twenty clinical trials of patients not receiving thrombolytic or aspirin therapy, heparin was associated with a significant reduction of deep vein thrombosis, pulmonary embolism, recurrent myocardial infarction and cerebrovascular accidents. In the context of secondary prevention of myocardial infarction, the administration of a moderate dose of subcutaneous heparin resulted in a beneficial effect on morbidity and mortality in one published trial. The use of low molecular weight heparins for the prevention of coronary thrombosis merits attention because of the pharmacological and pharmacokinetic properties of these products.