Single-chamber ventricular cardioverter-defibrillator (ICD) has been shown to significantly reduce the incidence of sudden cardiac death due to malignant ventricular arrhythmias. However, inappropriate therapy due to supraventricular tachyarrhythmias (mainly atrial fibrillation) affects up to 34% of patients. Moreover, it has been estimated that up to 20% of ICD patients are in the need of physiological antibradycardia pacing. Use of dual-chamber ICD offers an atrial signal for better ability to discriminate atrial from ventricular tachyarrhythmias as well as a maintenance of AV synchrony, what may be of critical importance for patients with a compromised left ventricular function. In the present study we describe our preliminary clinical experience with a dual-chamber ICD's implanted in 20 patients. During the implantation and in-hospital testing, 95 induced VT/VF episodes were correctly diagnosed by ICD, as well as 28 induced FA episodes. Over a mean follow-up period of 10 +/- 6 months, 98 tachycardia episodes were recorded. All 76 VT/VF episodes were correctly diagnosed, as were 18 of 22 FA. Four FA episodes were diagnosed as VT/VF and treated by antitachycardia pacing in 2 cases and by shock in 2. Thus, sensitivity and specificity of VT/VF detection are 100% and 82% respectively. A dual-chamber ICD appears to improve discrimination of atrial from ventricular tachyarrhythmias without loss of sensitivity and to decrease occurrence of inappropriate therapy. AV synchrony, by improving the hemodynamic status of the patient (mainly in those with impaired left ventricular function), may demonstrate better survival and comfort of life.