Cardiac diseases in sports horses represent a significant cause of poor performance. In sport horses, we find anatomical and physiological adaptations of the cardiovascular system that are necessary considering the demands of the sport. An increase in heart size, as well as the capacity of the spleen, but also a reduced response to lactate in the muscles, increased stroke volume and heart frequency enable efficient work of the cardiovascular system at maximum capacity. Of the heart diseases found in sports horses, murmurs and arrhythmias are of importance. We consider murmurs to be diseases that manifest themselves as murmurs upon auscultatory examination. Common diseases that cause murmurs in sport horses are mitral insufficiency, aortic insufficiency, tricuspid insufficiency, and ventricular septal defect. For the diagnosis of these diseases, we use ECHO, an ultrasound that allows us to examine the heart in real time. Another excellent method that can help us further confirm these diagnoses is color doppler, which allows us to see the direction of blood flow in the heart. Arrhythmias that are common in sport horses are atrial fibrillation (one of the most common heart diseases in sport horses), 2nd degree AV block, and supraventricular and ventricular arrhythmias. For the diagnosis of arrhythmias, the gold standard is the ECG, which can be used to monitor the heart's rhythmicity. To confirm it is in fact a heart pathology, we can repeat the ECG (over 24 hours – with a Holter ECG, or with an endurance test) and compare the obtained results to get a clearer picture of the action and rhythmicity of the heart in various conditions. The prognosis depends on the expectations and requirements we have from the horse. Sport horses (especially in disciplines where they work at HR max) have a much worse prognosis compared to recreational horses with the same diagnoses. Treatment is challenging since it often requires rest and a reduction of training, which is usually not an option for sport horses, but for diseases in the initial stages or less advanced cases, treatment is more successful, and the prognosis is relatively good. Unfortunately, some drugs that are currently available for the treatment of these diseases have side effects, and other treatment methods, such as transverse electrical cardioversion, represent a more complex and expensive alternative.