Heart valve called the "semilunar valves". These two arteries receive blood from the ventricles and their semilunar valves permit blood to be forced into the arteries, and prevent backflow from the arteries into the ventricles. These valves do not have chordae tendineae, and are more similar to the valves in veins than they are to the atrioventricular valves. The closure of the semilunar valves causes the second heart sound. The aortic valve, which has three cusps, lies between the left ventricle and the aorta. During ventricular systole, pressure rises in the left ventricle and when it is greater than the pressure in
Short QT syndrome activation lose their pumping ability - fibrillation of the cardiac atria in atrial fibrillation leads to an irregular pulse, and fibrillation of the cardiac ventricles in ventricular fibrillation renders the heart unable to pump blood at all. There are several possible mechanisms by which short action potentials might promote fibrillation. The link between these mechanisms is how the duration of the action potential influences how frequently a heart muscle cell can be excited. A shorter action potential generally allow a heart muscle cell to be excited more frequently - the refractory period is shorter. The first mechanism, referred to as