The left ventricular ejection fraction (LVEF) is one of the most studied and widely used indicators in clinical practice for assessing the prognosis and functional capabilities of patients with cardiovascular diseases. The systolic function of the left ventricle can significantly decrease with prolonged coronary heart disease, especially with the development of acute coronary syndrome, even despite timely endovascular revascularization of the myocardium, the appointment of optimal drug therapy, and early cardiac rehabilitation. Aim: Assessment of the effect of LVEF on the level of exercise tolerance based on the results of exercise tests in patients with acute coronary syndrome after endovascular myocardial revascularization at the inpatient stage of treatment. Materials and Methods: 206 patients with acute coronary syndrome were examined (Acute ST-segment elevation myocardial infarction - 113 patients, Non–ST-segment elevation myocardial infarction - 93 patients), the average age was 60.6±10.9 years. 133 patients with preserved LVEF (?50% according to Simpson) and 73 patients with moderately reduced LVEF (40-49% according to Simpson). Before the end of the inpatient treatment stage, stress tests were performed (the symptom-limited bicycle ergometry and a six-minute walking test), according to the results of which patients were stratified according to the level of exercise tolerance. Results: Differences in the parameters of stress tests performed in the early stages of treatment and rehabilitation of patients with acute coronary syndrome in groups with different LVEF determined differences in the level of exercise tolerance stratification. More than half - 83 (62,4 %) patients with preserved LV contractile function had high and moderate LVEF, whereas in the group with moderately reduced LVEF, the majority - 49 (67,1 %) patients had low exercise tolerance. Conclusions: The left ventricular ejection fraction in patients with acute coronary syndrome after endovascular revascularization is a predictor of exercise tolerance, which requires personalized approaches to the formation of physical cardio rehabilitation programs.