This study presents the acute and long-term results of 307 patients (267 men, mean age 57.5 years, 205 suffering from coronary artery disease, mean left ventricular ejection fraction 33.3%) with malignant ventricular tachyarrhythmias who underwent attempted transvenous ICD implantation with the CPI Endotak lead system in 37 Italian centers. Transvenous ICD implantation was ultimately accomplished in 306 (99.7%) patients. These included 19 subjects with high (< 10 J below output energy of implanted device) defibrillation threshold (DFT) at implant. One hundred sixty-four patients (53%) were implanted with the endocardial lead alone, while 142 also received an SQ patch or SQ array. The mean DFT (not always step-down DFT) at implant was 16.9 +/- 5.7 joules; 15.3 +/- 5.2 joules with biphasic shock and 19.6 +/- 5.4 joules with monophasic shock; P < 0.0001. A significantly higher percentage of patients tested with a biphasic shock could be implanted with adequate safety margin and without an additional SQ patch or SQ array (98% and 81%, respectively). No perioperative deaths occurred. During the mean follow-up of 14.5 +/- 10.2 months, 140 patients (52%) received at least one appropriate shock. An inappropriate shock was observed in 26% of episodes. The 1- and 3-year actuarial incidence of sudden death was 2% and 4%, respectively, and that of total death was 10% and 20%, respectively. A pocket infection requiring ICD explantation occurred in 4 patients (1.4%) and an endocardial lead dislodgment in 11 patients (3.6%). Two patients (0.3%) showed a sensing pin disconnection and six patients (2.3%) had a lead insulation break. The results of this Italian multicenter trial indicate that the CPI Endotak lead system is a simple, safe, and reliable system for endocardial defibrillation. When compared to epicardial leads, it clearly reduces the perioperative mortality and morbidity, while maintaining a similar efficacy in preventing sudden death and terminating ventricular arrhythmias.