Outline the circulation of blood and the physical changes of the heart during the cardiac cycle.

The cardiac cycle is split into 2 main phases: systole where the heart contracts and ejects blood out from the heart and diastole where the heart relaxes and fills with blood. The right side of the heart pumps blood to the lungs via the pulmonary circulation and the left side of the heart pumps blood to the rest of the body via the systemic circulation.
Circulation of blood through the right side of the heart:Deoxygenated blood returns from the body and fills the right atrium, this causes the pressure of the right atrium to rise. As the atrium contracts, the right atrial pressure eventually exceeds the pressure in the right ventricle, consequently opening the tricuspid valve. As a result, blood fills into the right ventricle. As the ventricles contract, the right ventricular pressure now exceeds the right atrial pressure causing the tricuspid valve to snap shut. This provides a clear pathway for blood to be pumped out of the right ventricle and into the pulmonary artery through the pulmonary valve. Blood is then directed to the lungs to be oxygenated.
Circulation of blood through the left side of the heart:Oxygenated blood re-enters the heart from the lungs into the left atrium (via the pulmonary vein). Similarly, the pressure of the left atrium increases as it fills with blood. Eventually, the left atrial pressure exceeds the left ventricular pressure, opening the bicuspid valve. Blood empties into the left ventricle (the thickest chamber of the heart) which gradually increases in pressure. Once the ventricles contract during systole, left ventricular pressure exceeds the left atrial pressure, thus closing the bicuspid valve and opening the aortic valve. Blood is forced out of the heart through the aortic valve and into the aorta where it can be distributed to the rest of the body.