Mechanisms and causes of hyperglycemia (HG) during coronary heart disease (CHD), particularly in its unstable forms, remain not fully investigated. The study aimed to determine the effect of newly detected HG on the course of CHD and examine the features of carbohydrate metabolism in patients with CHD. The study was conducted in Moscow (Russia) in 2018-2021. A total of 139 patients with CHD aged 43 to 79 years were examined. All participants were divided into comparison groups, including 34 patients with average glucose levels, 28 patients with fasting HG, 46 patients with impaired glucose tolerance (IGT), and 31 patients with newly diagnosed type 2 diabetes. The range of laboratory examinations included general clinical tests of blood and urine, determination of blood urea, creatinine, C-reactive protein, bilirubin and its fractions, the activity of hepatic transaminases, the study of carbohydrate metabolism, lipidogram, ionogram, and coagulogram. First-time diagnosed HG was a fairly frequent diagnosis in CHD patients (in 105 (75.5%) of 139 patients examined). IGT and type 2 diabetes mellitus recently detected in CHD patients have common disease-causing factors: insulin resistance, lipid metabolism disorders, and sympathetic nervous system activation against the background of reduced parasympathetic effects. All of this should be considered in developing treatment regimens for CHD patients and controlling risk factors.