The heart is made up of four chambers: the upper two being the right and left atria; and the lower- right and left ventricles. The right atria and ventricle are separated from the left atria and ventricle via the septum, a muscular partition between the two sides.
Right Atrium receives de-oxygenated blood through the Superior Vena Cava, from the head and upper body and via the Inferior Vena Cava from the lower torso and legs. It also receives blood from the coronary sinus, a collection of veins that assemble to form a large vessel that drains blood from the myocardium.
Left Atrium receives oxygenated blood from the lungs via the pulmonary veins.
Left Ventricle receives oxygenated blood as the left atrium contracts. It is responsible for pumping blood into the Systemic circulation round the body.
Right Ventricle receives de-oxygenated blood as the right atrium contracts. It is responsible for pumping blood into the pulmonary circulation to the lungs.