When an action potential is formed at the sino-atrial nodes (SAN), atrial contraction or systole occurs, which is followed by ventricular systole, atrial diastole, and finally ventricular diastole.
All four chambers of the heart are relaxed before the start of a cardiac cycle, known as joint diastole.
Steps of cardiac cycle:
Diastole and systole are the two phases of the heart cycle.
The diastole is when blood from the superior and inferior Vena cava returns to the heart and flows into the right atrium.
The input of a high amount of blood raises the pressure in the right atrium, which likewise raises the pressure in the right ventricle.
The tricuspid valve opens as a result, allowing blood to flow into the right ventricle. The oxygenated blood from the lungs rushes into the left atrium, causing the left atrial pressure to rise. As the left atrial pressure rises, the mitral valve opens, allowing blood to flow into the left ventricle.
Blood flows from the two atria into their respective ventricles during the systole phase. The depolarization of the atria causes the atrial muscle to contract, resulting in blood flow.
When the ventricular muscle contracts and creates pressure in the ventricle, the semilunar valves open. The diastole phase begins when the heart muscle relaxes again.
