Athlete's heart syndrome is a set of clinical, electrocardiographic and echocardiographic changes found in the heart of serious athletes whose sports participation mostly includes long primary aerobic physical activities and actions. The main clinical changes that are essential in the medical distinction between athlete's heart syndrome from similar pathological conditions are sinus bradycardia and arrhythmia, atrioventricular delay in conducting signals, increase in cardiac muscle (especially the left ventricle), vasovagal syncope, presence of heart murmurs and electrocardiographic changes in ST-T wave. The above mentioned symptoms of the syndrome are more often among the male athletes, although they occur in very small extent among female athletes. Furthermore, athletes who specializes in endurance sports such as cycling, running, rowing, cross country skiing, etc., generally have more symptoms than others. The reason is the increased aerobic activity. Using diagnostic techniques (echocardiography, magnetic resonance imaging of the heart and electrocardiography) is still difficult to safely separate the symptoms of athlete's heart syndrome from symptoms of other pathological conditions such as right ventricular dysplasia, dilated cardiomyopathy, myocarditis and hypertrophic cardiomyopathy. Therefore, in the past, but today, the athlete's heart syndrome is considered a gray zone between the pathology and positive evolutionary adaptation to stress caused by intense aerobic physical activity.