Objective: To compare the cardiovascular risk of exercise in the morning and afternoon in patients with established heart disease.
Design: Retrospective cohort study.
Patients: Patients with established heart disease referred for participation in a comprehensive cardiac rehabilitation program.
Intervention: Supervised, submaximal exercise (1 hour three times per week) performed either in the morning (7:30 AM) or the afternoon (3 PM).
Main outcome: Documented cardiac events that occurred while patients were exercising in the rehabilitation programs.
Results: There were five cardiac events in 168,111 patient-hours of exercise in the morning, with an incidence of 3.0 +/- 1.3 events per 100,000 patient-hours. There were two events during the 84,491 patient-hours of exercise in the afternoon, for an incidence of 2.4 +/- 1.5 events per 100,000 patient-hours (not significant). The risk ratio of cardiac events during exercise in the morning compared with the afternoon was 1.27 (95% confidence interval, 0.25 to 6.55).
Conclusion: In patients with coronary artery disease, the incidence of cardiac events is low during regular, submaximal exercise whether performed in the morning or the afternoon.