A multicenter prospective study has been designed to determine whether participation in an exercise program which produces a significant training effect will affect the recurrence rate in men who have survived an initial myocardial infarction. The control group consists of subjects who participate in a program involving low intensity activities designed to avoid a significant training effect. The subjects will be followed for a period of 4 years and a reduction of 50 per cent in the risk of recurrence will be considered clinically significant. The criteria for entry, the method of allocation, the structure of the exercise program and method of assessing cardiorespiratory fitness are described.