We experienced 20 cases of superior septal approach (SSA) for mitral valve surgery from June 1992 to December 1995. From pre-operative coronary angiography, sinus node arteries (SNAs) were grouped into three types, branched from right coronary artery (RCA: 45%), from left circumflex (LCx: 35%), and from both RCA and LCx (Bilateral: 20%). And, in diameter, they were grouped into two groups, above 1 mm (80%) and below 1 mm (20%). There were no peri-operative deaths and complications associated with SSA. In acute post operative phase, atrial fibrillation, junctional rhythm, atrial flutter, and sino-atrial block were observed, especially in patients whose SNA branched from RCA, and were above 1 mm in diameter. In late follow-up, all patients' rhythm returned to pre-operative rhythm, although some cases became bradycardia less than 60 per-minute. Bradycardia was observed in patients whose SNA branched from RCA, and were above 1 mm in diameter. There may be relationship between post operative arrhythmia and division of large SNAs originated from RCA. We concluded that SSA is safe and excellent approach for mitral valve surgery, especially in patients who require reoperations and in patients with small LA, although we should consider the advantages of SSA versus the risks of post operative arrhythmia and bradycardia.