The cardiac cycle refers to the process when the heart moves blood throughout the entire body, supplying it with oxygenated blood (OB) and returning deoxygenated blood (DOB) to the lungs. The organ has four chambers: two atria in the upper half and two ventricles in the lower one. They, along with various veins and valves, are crucial to the cardiac cycle due to a meticulous system of connections.
The cardiac cycle, with its contractions and relations, occurs during one heartbeat, which is controlled by electrical impulses generated by heart nodes. The process involves the right atrium (RA), which receives DOB through the inferior and the superior vena cava, and the left atrium (LA), which obtains OB from pulmonary veins. When the atria are relaxed, the ventricles receive both OB and DOB. The heart cavity has four valves: the tricuspid valve exiting from the RA, the pulmonic valve from the RV, the mitral valve from the LA, and the aortic valve from the left ventricle (LV). They are often called the great vessels, and each is connected to a certain chamber, acting as a one-way passage to prevent the reversed blood flow.
The circulation process starts when the RA contracts blood passing through the tricuspid valve into the RV. Afterward, the tricuspid valve closes, and blood continues moving inside the pulmonary arteries towards the lungs. The LA contracts it through the mitral valve into the LV; then, the former closes, and the blood passes the aortic valve to reach the aorta and its branches. Overall, the great vessels play an essential role in the cardiac cycle.