Objective    To investigate the polymorphism of Vitamin K epoxide reductase complex subunit 1 (VKORC1-1639A/G) in patients with mechanical heart valve prostheses as well as the possible relationship between the individual warfarin dosage requirements and this genetic polymorphism in Chinese patients in Chongqing region.     Methods    The polymorphism of VKORC1-1639A/G in 100 patients with mechanical heart valve prostheses operated in our department from September 1987 to October 2007 was detected by using PCR-RFLP and restriction enzyme digestion. The genotype and allelic frequencies were calculated and the individual warfarin dosage requirements were analyzed.     Results    In this group of patients VKORC1-1639A allele and VKORC1-1639G were detected

The frequency of A allele and G allele was 92% and 8% respectively. Three genotypes were detected too. AA was the most common genotype

with the frequency of 86%. The frequency of AG was 12% and the frequency of GG was less than 2% in these 100 patients. To achieve similar target INR range (1.5 to 2.5)

variant VKORC1-1639G homozygotes or heterozygotes required higher daily mean maintain doses (5.27±0.55 mg) than wildtype VKORC1-1639AA patients did (2.41±0.75 mg). VKORC1-1639A/G polymorphism is associated with warfarin dose requirements in 100 patients with mechanical heart valve prostheses receiving long-term therapy and showing stable control of anticoagulation in Chongqing region.     Conclusion    Polymorphism of VKORC1-1639A/G is dominant factor causing difference of individual warfarin dosage requirements (P0.01). 