Cardiac resynchronization through atrio-biventricular pacing has recently been introduced for patients with drug refractory heart failure and intraventricular conduction delay. Left ventricular pacing can be achieved by positioning pacing leads into the cardiac veins through the coronary sinus. In the InSync Italian Registry 190 patients from 39 Italian centres have been enrolled and prospectively followed. Technique reliability, patient selection, ventricular function improvement and clinical outcome have been evaluated. The implant success rate was 89%. Specifically designed leads, dedicated guide catheters and coronary sinus angiography were used in the majority of patients. The mean implant procedure duration was 2.63 ± 1.13 h and the mean fluoroscopy time 37.32 ± 27.86 min. The most common left ventricular lead final positioning was the posterolateral wall. Pacing threshold and impedance and R wave sensing were good and remained stable during 1 year of follow-up. Complications included cardiac tamponade (0.9%), pericardial effusion (0.9%), and cardiac arrhythmias (2.8%). The left ventricular lead dislodgement rate was 7.4%. After implantation, the QRS width decreased from 177 ± 29 ms to 136 ± 22 ms (P<0.0001) and interventricular mechanical delay from 55 ± 27 ms to 25 ± 22 ms, (P<0.0001). On the basis of the Registry data, ventricular resynchronization can be effectively obtained transvenously with an acceptable complication rate. Technological progress is needed to enhance implant success rate, to shorten procedure duration and to increase patient tolerance.