Heart rate date normally used to date pregnancy in the medical community. The electrical depolarizations that trigger cardiac myocytes to contract arise spontaneously within the myocyte itself. The heartbeat is initiated in the pacemaker regions and spreads to the rest of the heart through a conduction pathway. Pacemaker cells develop in the primitive atrium and the sinus venosus to form the sinoatrial node and the atrioventricular node respectively. Conductive cells develop the bundle of His and carry the depolarization into the lower heart. The human heart begins beating at a rate near the mother’s, about 75–80 beats per minute (bpm). The embryonic
Isovolumetric contraction maintain the correct unidirectional flow of blood through the heart and circulatory system. The word contains the prefix iso-, derived from the Ancient Greek ἴσος (ísos), meaning equal. Therefore, an isovolumetric contraction is one in which the volume of fluid remains constant. Isovolumetric contraction In cardiac physiology, isovolumetric contraction is an event occurring in early systole during which the ventricles contract with no corresponding volume change (isovolumetrically). This short-lasting portion of the cardiac cycle takes place while all heart valves are closed. In a healthy young adult, blood enters the atria and flows to the ventricles via the opened atrioventricular