Background and aims: The aim of this study was to explore potential associations of the intron 4 variable number of tandem repeats (VNTR) and E298A polymorphisms of the endothelial nitric oxide synthase (eNOS) gene with slow coronary flow (SCF). The association between plasma nitrate and nitrite (NOx) concentrations and eNOS gene polymorphisms was also assessed. Materials and methods: The intron 4 VNTR and E298A polymorphisms of the eNOS gene were evaluated in the isolated DNA blood samples obtained from the SCF patient group (n = 30) and healthy group consisted of age- and sex-matched controls (n = 61). Results: Plasma NOx level was significantly lower in patients with SCF than in controls. In addition, patients with SCF have significantly lower nitric oxide levels than control subjects within each genotype variants. The allele and genotyped frequencies of the eNOS intron 4 VNTR and E298A polymorphisms were similar between patients with SCF and the controls. Plasma NOx concentrations with respect to the relevant genotypes were found insignificant. Discussion and conclusion: Plasma NOx is lower in patients with SCF than in healthy subjects. Our findings may suggest the lack of association between intron 4 VNTR and E298A polymorphisms of the eNOS gene and SCF.