Objective   To study the correlation between CYP2C9  *1 and *3 mutations and Warfarin dosage in patients after replacement of mechanical heart valve in Chongqing area.  Methods   CYP2C9 *1 and *3 mutations were detected in 100 patients after replacement of mechanical heart valve by PCR-RFLP. Mutation frequencies of CYP2C9 *1 and *3 genes and allelic genes were calculated. Two Warfarin concentrations were measured in the patients by HPLC with related clinical parameters recorded.  Results   Two genotypes

CYP2C9 *1/*1 and CYP2C9 *1/*3

were detected in the patients after treatment with Warfarin in Chongqing area

with a frequency of 95% and 5%

respectively. No CYP2C9 *2 and CYP2C9 *3/*3 were detected. After INR reached 1.5-2.5

the patients with CYP2C9 *1/*3 and CYP2C9 *3/*3 were treated with Warfarin at maintenance dose of (2.67±0.95)mg and (2.67±1.10)mg

respectively (P0.05). The stable Warfarin concentration was (1 640.95±287.89) ng/ml for patients with CYP2C9 *1/*3 and (805.50±329.77)ng/ml for those with CYP2C9 *3/*3 (P0.01).  Conclusion   The dose of Warfarin is not related with CYP2C9  *1 and *3 mutations in patients after replacement of mechanical heart valve. However

the stable Warfarin concentration is related with CYP2C9 *1 and *3 mutations in patients after replacement of mechanical heart valve. Detection of CYP2C9 *1 and *3 mutations is of great importance in predicting the complications of anticoagulation treatment with Warfarin.