Changes in body composition have been studied in patients with ischemic heart disease over a 2-year period, commencing 3–12 months after a well-documented myocardial infarction. Findings have been related to diet, the exercise undertaken (random allocation of volunteers to high intensity and low intensity exercise programmes) and the recurrence of myocardial infarction. When first recruited, subjects were not much more obese than other middle-aged men. In contrast with experience in the ‘healthy’ middle-aged exerciser, compliance of postcoronary patients with the required regimen was uninfluenced by body build. Over the 2 years of observation, both high and low intensity exercise groups showed small losses of fat and gains of lean mass. It is suggested that these changes reflect responses to dietary regulation and an increase of physical activity rather than a specific effect of the prescribed effort; the potential advantage of the high intensity exercise programme was lost through a larger food intake. Patients who sustained a recurrence of their infarction had an average percentage of body fat, but a low excess weight and lean mass; although isometric exercise is not frequently implicated in the recurrence of an infarction, the development of muscle mass might be advantageous to patients who must continue to work in occupations that demand sustained isometric muscular activity.