How does the heart pump oxygen around the body?

Our heart can be divided into a left and right side, each containing two chambers: an atrium and a ventricle. Low pressure blood flows into the atria and is pumped out of the ventricles (high pressure); these two are connected by valves. We have a double circulatory system, composed of the systemic and pulmonary circuits. On the right side of the heart, deoxygenated blood enters the right atrium through the vena cava and is pumped out of the right ventricle to the lungs – this is through the pulmonary artery, which splits off into two branches. Oxygenated blood comes back from the lungs and re-enters the heart through the pulmonary vein into the left atrium. This is the pulmonary circuit between the heart and the lungs. Oxygenated blood is then pumped out by the left ventricle to the rest of the body – through the aorta, the largest artery we have. Arteries are under higher pressure and carry the blood away from the heart, whereas veins are under lower pressure and bring blood back towards the heart. After delivering oxygen to the tissues in the body, deoxygenated blood returns through the veins and into the heart through the vena cava, completing the systemic circuit between the heart and body.