Aims:The aim of this randomised clinical trial was to assess a comprehensive cardiac rehabilitation intervention including exercise training and psycho-education vs 'treatment as usual' in patients treated with an implantable cardioverter defibrillator (ICD).Methods:In this study 196 patients with first time ICD implantation (mean age 57.2 (standard deviation (SD)=13.2); 79% men) were randomised (1:1) to comprehensive cardiac rehabilitation vs 'treatment as usual'. Altogether 144 participants completed the 12 month follow-up. The intervention consisted of twelve weeks of exercise training and one year of psycho-educational follow-up focusing on modifiable factors associated with poor outcomes. Two primary outcomes, general health score (Short Form-36 (SF-36)) and peak oxygen uptake (VO2), were used. Post-hoc analyses included SF-36 and ICD therapy history.Results:Comprehensive cardiac rehabilitation significantly increased VO2 uptake after exercise training to 23.0 (95% confidence interval (CI) 20.9-22.7) vs 20.8 (95% CI 18.9-22.7) ml/min/kg in the control group (p=0.004 (multiplicity p=0.015)). Comprehensive cardiac rehabilitation significantly increased general health; at three months (mean 62.8 (95% CI 58.1-67.5) vs 64.4 (95% CI: 59.6-69.2)) points; at six months (mean 66.7 (95% CI 61.5-72.0) vs 61.9 (95% CI 56.1-67.7) points); and 12 months (mean 63.5 (95% CI 57.7-69.3) vs 62.1 (95% CI 56.2-68.0)) points (p <0.05). Explorative analyses showed a significant difference between groups in favour of the intervention group. No significant difference was seen in ICD therapy history.Conclusion:Comprehensive cardiac rehabilitation combining exercise training and a psycho-educational intervention improves VO2-uptake and general health. Furthermore, mental health seems improved. No significant difference was found in the number of ICD shocks or anti-tachycardia pacing therapy.