The goal of this prospective study was to examine the effects of landiolol hydrochloride on prevention of atrial fibrillation and on hemodynamics in the acute postoperative phase after heart valve surgery. The subjects were 60 patients who underwent valve surgery at our hospital from April 2008 to July 2010. The patients were randomly divided into two groups: the landiolol group (30 patients) and the control (no landiolol) group (30 patients). In the landiolol group, continuous intravenous landiolol was initiated immediately on admission to the intensive care unit at a dose of 10 µg/kg/ minute. Occurrence of atrial fibrillation was compared between the groups over an observation period of 72 hours after surgery. Atrial fibrillation occurred in 6 patients (20%) in the landiolol group and 16 (53.3%) in the control group during the observation period. Landiolol hydrochloride significantly reduced the occurrence of atrial fibrillation in the acute postoperative phase after heart valve surgery. Heart rate was significantly decreased by landiolol, but aggravation of hemodynamics was not observed. These results suggest that landiolol is a useful drug for prevention of atrial fibrillation after valve surgery.