Mitral valve exposure is widely improved by the superior-transseptal approach (STS). The diffusion of this technique has been restricted because of the possibility of detrimental effects of sino-atrial arrhythmias, especially in patients in sinus rhythm preoperatively. Between April 1991 and December 1992, we performed mitral valve replacement (MVR) on 55 patients by an STS approach. The mean age was 57.7 +/- 11.3 years (38-75 years). 21 were reoperations and 1 patient had been operated twice. The procedure consisted in 10 MVR with a bioprosthetic valve and 45 with a mechanical valve. Associated procedures were 5 tricuspid annuloplasties, 13 aortic valve replacements, 1 tricuspid valve replacement, 4 CABG, and 1 aneurysm resection. Overall hospital mortality was 9.1 +/- 3.8% (5/55). Mortality for isolated MVR was 6.2 +/- 4.2% (2/32). 51% (28/55) were in sinus rhythm (SR) preoperatively, 43% (12/28) of them had never presented atrial fibrillation. Postoperatively among those 28 patients in SR, 20 remained in SR, 7 were in atrial fibrillation, and 1 in atrial flutter. 3.6% (2/55) needed transient electrosystolic pacing for very slow atrial fibrillation 20% (11/55) have presented a transient sino-atrial dysfunction; None of these rhythmic events had any adverse effect. Finally, the very good visibility and accessibility are the major advantages of this approach, especially in mitro-tricuspid combined procedures, in small left atrium and repeat surgery. As sino-atrial arrhythmias are transient, we think this approach can be routinely employed in MVR.