Patients with an implanted cardioverter defibrillator (ICD) commonly avoid exercise due to concerns regarding a possible increase in the number of shocks being deployed. Methods: We searched Medline and EMBASE for randomised controlled trials comparing aerobic exercise training (EX) versus no-exercise (NO-EX) in patients with an ICD. From each study, we compared pre to post-intervention change in peak oxygen uptake (VO2peak) and the number of patients receiving shocks within each group during follow-up. Outcomes were pooled using random-effects meta-analysis. Results: 408 studies were identified, five of which met our inclusion criteria. Data from 1352 individuals (mean age: 60 yrs; LVEF 31%) over a mean follow-up of 1.6 years contributed to this analysis. Mean EX program duration was 10 weeks (range: 8-12) with a mean frequency of 3.5 sessions per week (range: 3-5). Three studies prescribed moderate intensity, continuous aerobic exercise, one incorporated moderate intensity isometric activities, whilst one incorporated intermittent, high-intensity bouts of exercise. Patients randomised to EX increased VO2peak significantly more than NO-EX (Mean difference: 2.0 ml/kg/min, 95% CI: 0.59-3.40, p=0.005). There was significant heterogeneity for VO2peak as the outcome variable (12=96%, p<0.001). In the EX group, 16.5% of patients received shocks, compared to 20.9% in the NO-EX group (OR 0.46, 95% CI 0.19-1.13, p=0.09). Conclusions: Patients with an ICD achieve significant improvements in aerobic capacity following exercise without any concomitant increase in the shocks. These findings support the prescription of moderate aerobic exercise in patients with an ICD. (Table Presented).