The 27-bp tandem repeat polymorphism in intron 4 of the endothelial nitric oxide synthase gene (eNOS) in populations of the Volga-Ural region was studied by means of polymerase chain reaction. In Russians and Tatars, the possible association of this polymorphism with coronary heart disease complicated by either myocaridal infarction or by essential hypertension was examined. Russians with essential hypertension associated with hypertrophy of the left ventricle displayed a statistically significant increase of the eNOS4A/B genotype and the A allele frequencies along with the decrease of the frequencies of the eNOS4B/B genotype and the B allele. In Tatars survived from myocardial infarction and with the risk of cardiovascular diseases (smoking or burdened heredity), a statistically significant increase of the frequencies of the eNOS4A/B genotype and the A allele was observed. Thus, in Russians the eNOS4A/B genotype was associated with the development of essential hypertension, while in Tatars it was associated with the risk of myocardial infarction.