The right side carries deoxygenated blood from the body to the lungs. The left side carries oxygenated blood from the lungs to the body. The septum keeps the two apart.

Deoxygenated blood from the body enters the right atrium through the vena cava, passes the atrioventricular valve into the right ventricle, and is pumped through the semilunar valve into the pulmonary artery to the lungs. Oxygenated blood returns from the lungs in the pulmonary vein to the left atrium, passes the atrioventricular valve into the left ventricle, and is pumped through the semilunar valve into the aorta to the body. Blood is pumped away from the heart in arteries and returns to the heart in veins — that is the blue and red flow you can watch in the model.

The atria contract first and push blood down into the ventricles. Then the ventricles contract and force blood out into the arteries. The one-way valves make sure blood only moves forwards: the atrioventricular valves close as the ventricles contract (the "lub"), and the semilunar valves close as the ventricles relax (the "dub"), stopping blood falling back.

The left ventricle pumps blood all around the body, so it needs a higher pressure and therefore a thicker, more muscular wall. The right ventricle only pumps blood to the lungs, which are close by and would be damaged by high pressure. The atria have the thinnest walls of all — they only push blood a short way down into the ventricles.

Coronary heart disease is the blockage of the coronary arteries, so the heart muscle no longer gets enough oxygenated blood. The possible risk factors are diet, lack of exercise, stress, smoking, genetic predisposition, age and sex. A balanced diet (less saturated fat and salt) and regular exercise both help reduce the risk.

Blood passes through the heart twice for each circuit of the body: once to the lungs and back, and once around the body and back. This keeps the pressure high, so blood flows to the body faster than it would in a single circulation.

The atrioventricular valves sit between each atrium and ventricle. The semilunar valves sit where the arteries leave the ventricles. The syllabus asks for these two names only — not "tricuspid" or "bicuspid".