A controlled trial of community based coronary rehabilitation. Two hundred patients who had suffered an acute myocardial infarction 4-6 weeks before entered a randomised controlled trial of exercise treatment at a community sports centre supervised by a general practitioner. Eighty one per cent of the treatment group continued to exercise until they returned to work and 73% completed three months' exercise. There were no serious complications of the exercise course. The prevalence of angina pectoris fell by 10% in the treatment group but rose by 60% in the control group. The perceived energy level rose by significantly more in the treatment group than in the controls. The rise in predicted maximum oxygen uptake was significantly greater in the treatment group than in the control group as was the reduction in the double product (a reflection of myocardial workload) at peak exercise. Coronary rehabilitation in the community can be both safe and effective. 