Importance: Although nonparticipation in cardiac rehabilitation is known to increase cardiovascular mortality and hospital readmissions, more than half of patients with coronary artery disease in Europe are not participating in cardiac rehabilitation. Objective: To assess whether a 6-month guided mobile cardiac rehabilitation (MCR) program is an effective therapy for elderly patients who decline participation in cardiac rehabilitation. Design, Setting, and Participants: Patients were enrolled in this parallel multicenter randomized clinical trial from November 11, 2015, to January 3, 2018, and follow-up was completed on January 17, 2019, in a secondary care system with 6 cardiac institutions across 5 European countries. Researchers assessing primary outcome were masked for group assignment. A total of 4236 patients were identified with a recent diagnosis of acute coronary syndrome, coronary revascularization, or surgical or percutaneous treatment for valvular disease, or documented coronary artery disease, of whom 996 declined to start cardiac rehabilitation. Subsequently, 179 patients who met the inclusion and exclusion criteria consented to participate in the European Study on Effectiveness and Sustainability of Current Cardiac Rehabilitation Programmes in the Elderly trial. Data were analyzed from January 21 to October 11, 2019. Interventions: Six months of home-based cardiac rehabilitation with telemonitoring and coaching based on motivational interviewing was used to stimulate patients to reach exercise goals. Control patients did not receive any form of cardiac rehabilitation throughout the study period. Main Outcomes and Measures: The primary outcome parameter was peak oxygen uptake (Vo₂peak) after 6 months. Results: Among 179 patients randomized (145 male [81%]; median age, 72 [range, 65-87] years), 159 (89%) were eligible for primary end point analysis. Follow-up at 1 year was completed for 151 patients (84%). Peak oxygen uptake improved in the MCR group (n = 89) at 6 and 12 months (1.6 [95% CI, 0.9-2.4] mL/kg^-1/min^-1and 1.2 [95% CI, 0.4-2.0] mL/kg^-1/min^-1, respectively), whereas there was no improvement in the control group (n = 90) (+0.2 [95% CI, -0.4 to 0.8] mL/kg^-1/min^-1and +0.1 [95% CI, -0.5 to 0.7] mL/kg^-1/min^-1, respectively). Changes in Vo₂peak were greater in the MCR vs control groups at 6 months (+1.2 [95% CI, 0.2 to 2.1] mL/kg^-1/min^-1) and 12 months (+0.9 [95% CI, 0.05 to 1.8] mL/kg^-1/min^-1). The incidence of adverse events was low and did not differ between the MCR and control groups. Conclusions and Relevance: These results suggest that a 6-month home-based MCR program for patients 65 years or older with coronary artery disease or a valvular intervention was safe and beneficial in improving Vo₂peak when compared with no cardiac rehabilitation. Trial Registration: trialregister.nl Identifier: NL5168.