Surgical treatment of atrial fibrillation (AF) using a variety of energy sources and a mixture of lesion sets has become an important adjunct in patients undergoing cardiac surgery. We retrospectively analyzed prospectively collected data of 141 patients with a history of AF (mean duration of AF 35+/-39 months; intermittent AF: n=72; 51%; permanent AF: 69 (49%)) who underwent a left-sided Cryomaze procedure in conjunction with mitral valve (MV) surgery between January 2003 and September 2006. Freedom from AF was 77% at discharge and 87% at a mean follow-up of 305+/-195 days with a decreasing rate of AF during the first 3-9 months from 13% to 9% and an increase beyond the first year (29% at 2 years). Predictors of failed Cryomaze in multivariate analysis were left atrial size >50 mm (OR=5.7), AF at surgery (OR=5.0) and cardiac reoperation (OR=3.4), whereas preoperative beta-blocker treatment was a predictor of success (OR=0.2). Our data suggest that a left-sided Cryomaze procedure effectively restores sinus rhythm in patients with AF undergoing MV surgery. The success rate should not be evaluated immediately postoperatively because there is a steady increase in the rate of patients with freedom from AF in the first year. It appears, however, that there is a higher rate of recurrence during later follow-up.