To evaluate the effect of cardiac rehabilitation and exercise training on depression after major cardiac events, we studied 338 consecutive patients in whom a major cardiac event had occurred 4 to 6 weeks previously and who were participating in phase II cardiac rehabilitation consisting of 36 sessions over a 3-month period. Depressive symptoms and other behavioral characteristics and quality-of-life parameters were analyzed by validated questionnaire. Depression was prevalent in patients with coronary heart disease, occurring in 20% of the patients evaluated. At baseline, depressed patients had lower exercise capacity, reduced high-density lipoprotein cholesterol level, and higher triglyceride levels; had lower scores for mental health, energy or fatigue, general health, pain, overall function, well-being, and total quality of life; and had greater scores for somatization, anxiety, and hostility than those of nondepressed patients. After cardiac rehabilitation, depressed patients had marked improvements in depression scores and other behavioral parameters (anxiety, somatization, and hostility) and quality of life. Depressed patients also showed improved exercise capacity, percentage of body fat, and levels of triglycerides and high-density lipoprotein cholesterol. Depressed patients exhibited statistically greater improvements in certain behavioral and quality-of-life parameters than did nondepressed patients. Two thirds of the patients who were initially depressed resolved their symptoms by study completion. In conclusion, depression is reduced in patients with symptomatic coronary heart disease patients enrolled in cardiac rehabilitation. Greater emphasis is needed to ensure that depressed patients are referred to and attend formal cardiac rehabilitation programs after major cardiac events.