A large prospective observational study of 4657 patients undergoing cardiac surgery demonstrated that postoperative use of angiotensin-converting enzyme inhibitor (ACEI) reduced the incidence of postoperative AF after cardiac surgery by 38%.111 Negative studies about the preventive effect of ACEIs and angiotensin receptor blockers (ARB) on postoperative AF have also been published. The gene discussed is ACE; the disease is atrial fibrillation.