Purpose: Despite strong recommendations and beneficial health effects of cardiac rehabilitation (CR), participation rates remain low. Little data are available on reasons beyond quantitative factors in the underutilization of CR. The aim of this study was to identify personal reasons for nonattenders and noncompletions of CR among Dutch and German patients with cardiovascular diseases (CVD) eligible for CR. Methods: Between December 2017 and January 2019, a total of 4265 questionnaires were distributed among eligible patients for CR in the bordering area of the eastern Netherlands and western Germany. Patients were eligible if they had an indication for CR according to national guidelines. Questionnaires were used to assess reasons of nonattendance and noncompletion of CR, when applicable. Results: A total of 1829 patients with CVD completed the questionnaire. Of these, 1278 indicated that they received referral to CR. Despite referral, 192 patients decided not to participate in CR and 88 patients with CVD withdrew from the CR program. The three most reported reasons for nonattendance were as follows: (1) did not need the supervision (56%, n = 108), (2) did not need the CR trajectory (55%, n = 105), and (3) already exercised regularly (39%, n = 74). The most reported reasons for noncompletion were as follows: (1) could no longer participate because of other physical problems (30%, n = 26), (2) did not need the CR trajectory (26%, n = 23), and (3) the CR program was not personal enough (23%, n = 20). Conclusions: Most patients had motivational or perceptive reasons for nonattendance or noncompletion to CR. These possible misconceptions as well as perceived shortcomings of traditional CR underline the need for adequate motivation, information, and more personalized solutions (eg, eHealth, home-based CR) to increase the uptake and completion of CR.