Platelets from 103 patients with chronic coronary heart disease were studied electron microscopically, cytochemically, fluorescence microscopically and with radionuclides. The platelets showed polymorphism indicated by diverse sizes, various content of alpha-granules in platelets, emergence of degenerative hyperosmiophilic forms. Shorter life cycle of the platelets was observed in line with a compensatory increase in the number of their immature forms. Abundance of reversibly and irreversibly activated and degranulated cells impaired platelet aggregation. These changes entailed rearrangement of platelet glycocalyx. The findings evidence noticeable structural shifts in platelets which diminish their resistance to factors stimulating atherogenesis and underlying aggravations of coronary heart disease.