Abstract Background A recent survey among Dutch cardiac rehabilitation centers demonstrated considerable between-center variations in the contents of exercise training programs. For patients entering cardiac rehabilitation, current guidelines recommend tailored exercise training programs based on patient characteristics and rehabilitation goals. Objective This study was to analyze to what extent these patient characteristics are determinants of variations in training programs. Design This was a prospective, observational study with cross-sectional measurements among 10 cardiac rehabilitation centers. Methods The following data were obtained about patients entering cardiac rehabilitation: referral diagnosis, rehabilitation goals, and exercise training variables. Primary outcomes were variations in total aerobic training time, intensity, and volume before and after case-mix correction for population differences between centers. Secondary outcomes were variations in other training characteristics and the role of exercise testing in the determination of training intensity. Also, the roles of diagnosis and training goals in determining aerobic training time and intensity were studied. Results Data from 700 participants were analyzed. There were significant variations between centers in all aerobic and most resistance training characteristics. For aerobic training intensity, time, and volume, great variations remained after case-mix correction. An exercise test was performed for 656 participants (93.7%) but was used to determine training intensity in only 344 (52.4%) of these participants. In most centers, referral diagnosis and rehabilitation goals were unrelated to aerobic training time or intensity. Limitations Some form of selection bias cannot be excluded because the competing centers represented a minority of Dutch exercise-based cardiac rehabilitation centers. Conclusions This study showed that the contents of training programs varied considerably between cardiac rehabilitation centers, independent of ...