The European multicenter prospective randomised study (PIC Study) collected 83 pts severely symptomatic from HOCM and refractory or intolerant to drugs. All were prospectively equipped with a dual-chamber pacemaker and followed for one year. They were randomised to three months each of active (DDDon) or inactive (AAI30 = DDDoff) DDD pacing in a blinded crossover study, followed by six months of permanent DDDon pacing. In all except 11 pts, pacing significantly reduced the pressure gradient and improved symptoms. Nineteen major adverse cardiac events were reported during this one year follow-up: 1 death, 1 subclavian vein thrombosis, 2 pneumothorax, 2 symptomatic pericarditis, 3 pocket infections, 10 lead dislodgements. The following arrhythmias were also reported. One ventricular and 1 atrial fibrillation(AF)occured during implantation. During the follow-up, 1 episode of paroxystic AF occured during pericarditis and six other episodes during the active mode (DDDon), two complicated by stroke. Conclusions: In this HOCM population, pacing was beneficial on pressure gradient and symptoms in 72 pts (87%). Despite a surprising number of complications, the pacemaker systems were functionning well in DDD pacing mode in these patients after one year follow-up. Therefore, pacing can be recommended in HOCM but must be strictly limited to a well selected population.