The aim of this study was ultrasound evaluation of atherosclerotic plaque morphology in relation to the degree of coronary artery lumen narrowing in patients with ischaemic heart disease. Intravascular ultrasound was performed on 38 patients (30 men and 8 women) aged 35 to 77 (average age 60 +/- 11 years old) with symptoms of ischaemic heart disease. The structure of atherosclerotic plaques with a degree of lumen narrowing of < 50% (1st group) was distinctly different from the structure of plaques with a degree of lumen narrowing of 50-75% (2nd group, p = 0.0045) and the structure of plaques with a degree of lumen narrowing of >/= 75% (3rd group, p < 0.001). The incidence of soft plaques decreased, whereas the percentage of mixed and hard plaques increased gradually with the increase in the degree of artery lumen narrowing. Significant differences in the incidence of plaque calcification were observed between the groups evaluated with crosssections of different degrees of lumen narrowing (p = 0.0032). The smallest number of calcifications was discovered in the 1st group as compared to the 2nd (p = 0.0027) and the 3rd group (p = 0.0026). With a higher degree of lumen narrowing, a lower percentage of eccentric plaques and a higher percentage of concentric plaques were observed. There were more eccentric plaques and fewer concentric plaques in cross-sections of the 1 st group as compared to the 2nd group (p = 0.0056) and the 3rd group (p = 0.0018). A comparison between the 2nd and 3rd groups showed no significant difference in the incidence of eccentric or concentric plaques (p = 0.5). In conclusion, intravascular ultrasound evaluation revealed significant relationships between the structure, presence of calcifications and location of atherosclerotic plaques and the degree of artery lumen narrowing. The incidence of mixed, hard, calcified and concentric plaques increased, whereas the percentage of soft, non-calcified and eccentric plaques decreased gradually with the increase in the degree of artery lumen narrowing.