Objective: The ideal prosthesis for aortic valve replacement in patients with small annuli remains controversial and has yet to be identified. The purpose of this report is to compare the St. Jude (SJ) Medical and Medtronic Hall (MH) valves for aortic valve replacement in the small aortic root. Methods: From 1986 to 1994 we prospectively randomized 456 patients to receive either the SJ or the MH valve. From this population, 80 patients (SJ, 42 patients; MH 38 patients) had a 19 or 21 mm aortic prosthesis inserted without annulus enlarging procedure. Results: Follow-up was complete in all 80 patients for 270 patient years (mean 40.5 months). Analysis showed that the SJ and MH groups were similar with respect to age, gender, body surface area, valve area, NYHA class, ventricular function, prosthesis size, frequency of revascularization, bypass and global ischemic time. There were two operative deaths (1 SJ, 1 MH). Clinical performance and Dobutamine stress transesophageal doppler echocardiography could not demonstrate a significant advantage of one prosthesis over the other in this population. The change in aortic valve gradient, and left ventricular mass index measured preoperatively and within 12 months postoperatively were not different in both cohorts. Conclusion: The study could not detect a difference in the performance of the SJ and MH heart valves for aortic valve replacement in patients with small aortic annuli. (C) 1997 Elsevier Science B.V.