Background Behavioral intervention studies in patients with an implantable cardioverter‐defibrillator (ICD) show promise in improving psychosocial outcomes but inconclusive effects on cardiovascular outcome. We assessed the effects of cognitive behavioral stress management (CBSM) on mood state and potentially arrhythmogenic cardiovascular responses to mental stress in ICD patients, in support of further larger scale arrhythmia trials. Methods A total of 103 ICD recipients were randomly assigned to 10‐week programs of CBSM or “Patient Education” (ED). Of these, 83 patients continued to either CBSM (n = 44) or ED (n = 39) intervention. Study end points were mood change, heart rate variability (HRV), double product elevation (DP = heart rate × systolic blood pressure) by math and anger‐recall stress, and arrhythmia up to 6 months follow‐up. Results Adjusting for multiple testing, CBSM was associated with moderate effect size reductions in tension/anxiety (P = 0.010), anger/hostility (P = 0.020), perceived stress (P = 0.037), and total mood disturbance (P = 0.025), greatest immediately following intervention (P < 0.05), and partially attributable to increased negative mood following ED (P < 0.01). No significant intervention effects on high frequency or low frequency spectral power of HRV, DP responses, or cardiac arrhythmias were demonstrated. Conclusions CBSM intervention in ICD recipients resulted in reduced anxiety, anger, and perceived stress, not sustained at 6 months follow‐up, and without conclusive effect on cardiac autonomic or hemodynamic responses to mental stress, or arrhythmia. Findings support conduct of larger behavioral intervention arrhythmia trial, with consideration of reinforcement training and targeting of subgroup responders to therapy.