Plaque complication depends on its composition and phenotype rather than on the degree of stenosis. Plaque rupture predominantly occurs in areas with large lipid core rich in cholesterol and thin fibrous cap. Features of unstable atheromas are mostly described in patients with acute coronary syndromes (ACS). The aim of our study was to assess the plaque characterization and arterial remodeling process in non-significant stenoses of patients with chronic coronary heart disease (CHD) using intravascular ultrasound (IVUS) radiofrequency (RF) data. Methods. The study included 22 stable patients (68% men, mean age 54+/-6 years) with CHD and clinical indications for coronary angiography (CAG). Diameter stenosis of the target coronary artery for IVUS procedure had to be less than 60%. Thin-cap fibroatheroma (TCFA) was defined as plaque burden >40% and amount of NC >10% without detectable overlying fibrous cap segment. Results. Sample size calculations based on the IVUS evaluation showed 54 atheromas in 29 target arteries. Features of vulnerability determined as TCFA were detected in 14 (26%) lesions. Compared with stable lesions VPs were associated with a greater plaque burden (48.5+/-8.0 mm2 vs 55.8+/-9.3 mm2, p=0.03), larger quantity of necrotic core (37.1+/-9.1% vs 24.0+/-12.6%, p=0.0045) and calcium content (22.7+/-8.5% vs 5.6+/-5.2%, p<0.000l), and less fibrous component (34.8+/-7.0% vs 60.4+/-12.4%, p<0.0001), respectively. Significant correlation was obtained between positive remodeling (defined as remodeling index >1.05) and NC percent area (r=0.389. p=0.005). Conclusion. In chronic CHD patients about 25% of atherosclerotic lesions responsible for less than 60% stenosis could be classified as vulnerable plaques. These borderline lesions contain more necrotic and calcium components compared with stable plaques, and are associated with positive arterial remodeling.