DNA replication is the process by which a double-stranded DNA molecule is copied to produce two identical DNA molecules.
The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right atrium and right ventricle.
The heart is a pump, and is composed of two upper chambers, the right atrium and the left atrium, and two lower chambers, the right ventricle and the left ventricle. Oxygen-depleted blood returns from the body via veins (superior vena cava and inferior vena cava), and fills up the right atrium with blood.