This study was undertaken to determine the incidence of postoperative arrhythmias in mitral valve surgery through the left atrium as compared with the extended trans-septal approach. All patients undergoing mitral valve surgery for acquired valve disease between 1 January 1991 and 31 December 1993 were reviewed. Only patients with preoperative normal sinus rhythm were included in this study. End-points for analysis were: 'any supraventricular arrhythmia'; 'atrial fibrillation of flutter'; and 'ectopic atrial or junctional rhythm'. All predictive factors with a P-value < 0.10 in univariate analysis were entered into the multivariate proportional hazard model of Cox. Some 72 patients were included for analysis. No variables were independently predictive of 'any supraventricular arrhythmia'. Age is an independent predictor of 'atrial fibrillation or flutter' and surgical approach of 'ectopic atrial or junctional rhythm'.