Abstract Background Pacemaker-dependent patients with left ventricular (LV) dysfunction benefit from upgrade to cardiac resynchronization therapy (CRT). Those at low risk for ventricular tachyarrhythmias may benefit similarly from a CRT-defibrillator or CRT-pacemaker. Objective To determine if coronary artery disease (CAD), because of associated scar that supports reentry, predicts higher risk of appropriate shocks in pacemaker-dependent patients upgraded to a CRT-defibrillator. Methods We grouped 157 pacemaker-dependent patients with LV ejection fraction (EF) ≤35%, no prior sustained ventricular arrhythmias, and conventional pacemakers upgraded to CRT-defibrillators by presence (n=75) or absence (n=82) of significant CAD. Overall survival, risk of appropriate shocks and anti-tachycardia pacing (ATP), complications related to high-power system components, and LVEF and end-systolic volume changes were contrasted between groups. Results Patients with CAD had more comorbidities and exhibited increased mortality during 59 ± 30 months follow-up (HR 2.55, 95% CI 1.49-4.36; p=0.001). Of 12 patients with appropriate shocks, 11 had CAD. Time to first shock, ATP, and tachyarrhythmia therapy were significantly shorter in CAD patients (p<0.01). The risk of an appropriate shock was 1 in 362 non-CAD patient-years vs. 1 in 26 CAD patient-years. Complications specific to high-energy device components necessitated another procedure in 32 patients (20%). LVEF improvement and end-systolic volume reduction were similar between groups. Conclusions Among pacemaker-dependent patients with no prior ventricular arrhythmias upgraded from a pacemaker to a CRT-defibrillator, those without significant CAD have fewer comorbidities, longer survival, and very low risk of appropriate shocks compared to CAD patients. CRT-pacemakers may be appropriate in such patients without CAD.