To examine the relationship between cardiac rehabilitation participation and health service expenditures in Ontario, Canada.A total of 6284 patients referred to cardiac rehabilitation between April 1, 2003, and December 31, 2010, were linked to 6284 matched cardiac rehabilitation eligible nonreferred controls and followed over a 3-year period across multiple linked administrative databases to identify health service utilization expenditures and mortality. All patients had previous cardiac hospitalizations within the preceding year. Four cardiac rehabilitation eligible groups of patients were balanced using propensity score weights: (1) no referral; (2) no participation; (3) low participation levels (ie, attending67% of prescheduled classes); and (4) high participation levels (ie, attending ≥67% prescheduled classes). Each group of patients was balanced in age, sex, geography, socioeconomic status, previous hospitalizations, ambulatory care conditions, cardiovascular risk factors, comorbidities, and previous health care expenditures. Generalized linear models were used to examine differences in health service expenditures (from all sources including hospitalizations, physician visits, diagnostic tests, and drugs for those older than 65 years) per "eligible day alive" over the 3-year period.Compared with the nonreferred population, health service expenditures followed a dose-response relationship and were lowest in patients who had the highest cardiac rehabilitation programmatic participation levels (P.001). Cost differences across groups separated early, remained divergent, and applied to all components of health care expenditures (P.001). Sensitivity analyses confirmed that the findings were not secondary to reverse causality.Participation in cardiac rehabilitation is associated with lower long-term health service utilization expenditures within a publicly funded health care system.