ardiac rehabilitation (CR) is a multidisciplinary, secondary prevention treatment modality 1 that reduces mortality and morbidity among patients with coronary heart disease and improves symptoms, functional capacity, metabolic status, depression, and health-related quality of life. 2,3 A recent analysis suggested that CR contributed significantly to the reduction in coronary heart disease mortality observed in the United States between 1980 and 2000 and that the risk reduction attributable to CR was comparable to reductions attributed to postevent aspirin, -blocker, angiotensinconverting enzyme inhibitor, statin, and warfarin therapy as well as to risk reductions attributed to acute thrombolysis and revascularization. 4 CR is considered a Class I indication after acute coronary syndrome, coronary revascularization, and for stable angina, but remains underutilized with low referral, low enrollment, and low completion rates and considerable disparities in access. 5,6 Article see p 677Many of the benefits of CR were demonstrated in clinical trials that predate contemporary treatments for coronary heart disease, in patient populations cared for in tertiary care settings, or in large administrative data sets which lack granularity regarding patients' clinical characteristics, disease severity, and concomitant therapy. 3,7,8 In this issue of Circulation, Martin et al 9 assessed mortality rates, hospitalizations, cardiac hospitalizations, and emergency department visits among 5886 individuals who had undergone cardiac catheterization, had detailed data collected at the time of the index event, and were referred to a single, centralized, communitybased CR program within 1 year of the index event. Median follow-up was 5.37 years. More than 40% of eligible patients who were referred chose not to attend, and an additional 9% enrolled but did not complete the program. Compared to CR completers, those who did not enroll or did not complete were older and sicker, more likely to be women, and more likely to be economically disadvantaged. CR completers had the lowest mortality rate, lowest hospitalization rates, and fewest emergency room visits. The relationship between CR completion and lower mortality rate was robust across unadjusted, adjusted, and propensity-matched analyses with hazard ratios between 0.57 and 0.67 for completers versus noncompleters. A similarly robust effect was seen for hospitalization rates, while there was no significant benefit of CR completion in relation to emergency room visits after adjustment for important covariates. Of note, individuals who enrolled in CR, but did not complete, had the highest rates of hospitalization and emergency room use and had mortality rates similar to those who chose not to attend. This study's major strength is the availability of detailed demographic and clinical information before CR enrollment and complete ascertainment of mortality and important health care utilization measures after enrollment achieved by linking several large databases. Through propensity-matchi...