During a 33-month follow-up of 1038 consecutive patients who had implantable cardioverter-defibrillators, appropriate shocks occurred in 329 of 1038 patients (32%). Appropriate shocks occurred in 101 of 380 patients (27%) treated with beta-adrenergic blockers alone; in 31 of 95 patients (33%) treated with amiodarone alone; in 39 of 149 patients (26%) treated with beta-blockers plus amiodarone; in 11 of 28 patients (39%) treated with sotalol alone; and in 147 of 386 patients (38%) treated with no beta-blockers, amiodarone, or sotalol (P < 0.001 comparing patients treated with beta-adrenergic blockers alone with patients treated with no beta-blockers, amiodarone, or sotalol; and P < 0.01 comparing patients treated with beta-blockers plus amiodarone with patients treated with no beta-blockers, amiodarone, or sotalol). In conclusion, patients having implantable cardioverter-defibrillators should also be treated with beta-adrenergic blockers to reduce the frequency of appropriate shocks.