Abstract: Objective To compare the change of left heart funct ion in pat ients w ith bio logical valves replacement of small ao rt ic roo t w ith mechanical valve rep lacement, and to find w hether there is p ro sthesis-patient mismatch (PPM ) or not after operation. Methods Left ventricular ejection fraction (LV EF ) , left ventricular fractional shortening (LVFS) , left vent ricular mass index, the indexed effective orifice area (EOA I) , and peak pressure gradients across aortic valve in 20 patients with small aortic root (≤21mm in diameter) receiving biological valves rep lacement (biological valves group ) were studied by Doppler echocardiography before the operation and 6 months to 1 year after operation. The results were compared with those of 20 patients who received mechanical valves replacement (mechanical valves group ). Results Comparing with those before operation, there was a significant increase in LVEF, LV FS, EOAI of all patients 6 months to 1 year after operation . There was a significant reduction in the left ventricular mass index, peak pressure gradients across aortic valve in all patients. EOAI of all patients were between 0.88 cm2/m2 and 1. 32 cm 2/m 2. LVEF, LVFS, EOAI, left ventricular mass index, and peak pressure gradients across aortic valve between biological valves group and mechanical valves group (79% ±8% vs. 81%±10%; 43%±9% vs. 37%±8%; 1. 11±0. 14 vs. 0. 92±0. 11; 89. 10±16. 70g/m 2 vs. 95. 30±15.10 g/m 2; 18. 80±12. 60 mmHg vs. 22. 30±12. 00 mmHg) showed no significant difference 6 months to 1 year after operation (P gt;0.05). Conclus ion Patients with small aortic root receiving biological valves have a significant increase in the left heart function, and have no PPM.