Objective To observe the intermediate-term outcome and heart function in patients with small aortic root，and to investigate the feasi bility of small size prosthesis. Methods From July 1990 to Jun e 2003, 62 patients underwent 19mm aortic valve prosthesis(19mm group). The resu lts were compaired with other 62 patients receiving larger prosthesis(≥21 mm,21 mm group). Clinical symptoms, signs, electrocardiogram(ECG) and echocardiogr a phy (UCG) were followedup, KaplanMeier survival curve was used for analysis. Results In 19mm group, there were 38 patients with ≥Ⅱ/Ⅵ grade systolic murmur in aortic valve area,18 patients with ECG ST segm ent change and 11 patients with chest pain and/or chest distress. Postoperative cardiac function showed that 33 patients with heart function New York Heart Ass ociation(NYHA) class Ⅱ and 29 patients with NYHA class Ⅲ. Postoperative ECG sh owed in 21mm group,6 patients with ECG ST segment change,3 patients with chest distress and 6 patients with occasional chest pain and there were 48 patients with NYHA class Ⅱ and 14 patients with NYHA class Ⅲ,there was statis tically difference in heart function between two groups（P＝0.020). Th ere was a significant regression of left ventricular end diastolic diameter(LVEDD),left ventricular wall thickness, mass index,and pressure gradients in both groups（P＜0.05）, and left ventricular ejection f raction (LVEF)had a significant increase in patients 5 years after operation tha n that before operation（P＜0.05）, and there was no statistically differenc e in both groups（P＞0.05）. Actual survival at 1,5 years were 93.5%,74 .2% in 19mm group compared with 95.2%,790% in the 21mm valve group, there were no statistically difference in both groups （P=0.231,0.110）. Conc lus ion Patients with 19mm prosthetic aortic valves can experience a satisf actory improvement and get excellent intermediate-term survival.