The normal heart is really two separate pumps working in tandem; there is no connection between the right and left sides in the normal post-fetal heart.
The right heart receives de-oxygenated blood from the body, moving it from the right atrium to the right ventricle to the lungs via the pulmonary artery. Carbon dioxide is released and oxygen is picked up in the lungs.
The left heart receives oxygenated blood from the lungs, moving it from the left atrium to the left ventricle, and from there to the aorta, which distributes it to the rest of the body.
The ventricles are thick muscular chambers which move blood with each contraction; the average left ventricle contracts with a force of 120 mmHg.