We report a single center's preliminary clinical experience of the Sentinel (Angeion, Minneapolis, MN) implantable cardioverter defibrillator (ICD), which employs novel technologies that offer the potential for significant reduction in ICD size. Thirty-three patients have received Sentinel ICDs with a mean follow-up of 450 (range 150-1023) days. Device shock therapy has been used to defibrillate/cardiovert 43 spontaneous episodes of malignant ventricular arrhythmia and 510 episodes of hemodynamically well tolerated ventricular arrhythmia have been pace-terminated (pace-termination failed in 6 episodes with subsequent delivery of appropriate shock therapy). There has been no arrhythmic death in this patient population. There have been 9 inappropriate shocks in 6 patients (in 2 patients for atrial fibrillation which had satisfied the algorithm detection criteria for high zone ventricular arrhythmia, in 3 for sinus tachycardia [rate greater than 180 beats per min] and in 1 due to device capacitor malfunction). Device replacement has been required for component malfunction in 3 patients. There have been no other major complications. Follow-up time to date is short and longterm device efficacy and performance remain unproven. However, our early clinical experience suggests that the innovations used to manufacture the Sentinel ICD have facilitated reduction in ICD size without compromising therapeutic efficacy.