OBJECTIVE: To determine the safety and effectiveness of a self-monitored, home-based phase II exercise program for high risk patients after cardiac surgery. METHODS: High risk patients were defined as those presenting with severe left ventricular dysfunction with an ejection fraction less than 35%, severe ventricular arrhythmias, incomplete revascularization, abnormal response to a standard walking test or significant (grade 3/4) valvular regurgitation persisting postoperatively. Eighty patients (mean age 58.5 +/- 8.9 years) were randomly assigned to two groups. The experimental group (n = 37) received a home program of aerobic training with an intensity gradually increasing from 1.5 to 4.0 multiples of resting oxygen consumption (METs). This program was started at discharge from the hospital and lasted eight weeks. The control group (n = 43) received general guidelines for progressive increase of their activity level. Functional capacity was measured at discharge by the 6 min walking test and between the sixth and eighth week following discharge by a symptom-limited exercise test, according to the Naughton protocol. RESULTS: No cardiovascular complications occurred during the training program. At the final evaluation, there was no significant difference between the experimental and control groups regarding aerobic capacity (5.1 +/- 1.8 versus 4.9 +/- 1.6 METs respectively, P = 0.61), nor peak rate-pressure product (22.8 +/- 4.9 versus 23.6 +/- 5.2 beats/min x mmHg x 10(3) respectively, P = 0.54).