Please explain the pathway of blood in the mammalian heart.

Blood enters the right side of the heart through the vena cava. In Humans this is divided into what we refer to as the superior and inferior vena cava. These terms essentially mean the top and bottom vena cava. The superior vena cava allows blood from the top half of the body to enter the heart and the inferior vena cava allows blood from the bottom half of the body to enter the right side of the heart. From the vena cava, the blood enters the right atrium, flows through the tricuspid valve when opened which prevents backflow of blood, into the right ventricle. Once in the right ventricle the blood is pumped out of the semi lunar valves through into the pulmonary artery. Here the blood is taken to the lungs to become oxygenated, and is returned via the pulmonary vein to the left side of the heart, specifically the left atrium. Blood then flows through the mitral valve, into the left ventricle where it is subsequently pumped out of another set of semi lunar valves into the aorta which has many branches and can distribute the oxygenated blood all around the rest of the body to organs.