The cardiovascular system is the most important system in the body. It is formed mainly of the heart which is responsible for pumping the blood throughout the big tree of blood vessels all over the body. The blood carries also nutrients and oxygen to whole body tissues and eliminates carbon dioxide and waste products. In order to protect the heart especially in the intraoperative period; we have to understand the anatomy of the heart including chambers, blood supply, and nerve supply and conducting system. Physiology of the heart includes the properties of cardiac muscle, mechanism of contraction and relaxation, and cardiac cycle. Pathophysiology of main cardiac diseases including IHD, HF and Arrhythmias should be always kept in mind.