How does the normal heart work?

The normal heart is composed of four chambers. The two upper chambers are reservoirs, which collect blood as it flows back to the heart. These are called "atriums".  From the Atriums blood flows into the lower two chambers, called "ventricles', which pump blood, with each heart beat, into the main arteries. From the right side of the heart one of these arteries (the Pulmonary Artery) carries blood into the circulation through the lungs. The left side of the heart, on the other hand, pumps blood into the other main artery (called the Aorta), which takes blood to the rest of the body.

The two ventricles and the two atriums are separated by partitions (called Septums). The partition between the Atriums is called the Atrial Septum (AS) and that separating the two ventricles the Ventricular Septum (VS). Dark (blue) blood returning to the right atrium from the body and its organs, through the two main veins (called the Superior and Inferior Vena Cavas), is pumped by the right ventricle to the lungs for replenishment with oxygen. The blue blood becomes bright red in the lungs when oxygen is replaced. This red blood returns, through two veins from each lung, to the left atrium and is pumped by the left ventricle  to the body again.

What are the heart valves?

There are four valves which control blood flow through the heart. They all comprise two or three flaps which swing open to allow blood through, with each beat, and swing back together to prevent blood going in the wrong direction. The valves are situated at the junction of the Atriums with the Ventricles (Tricuspid and Mitral valves) and at the origin of the major arteries from the ventricles (Pulmonary and Aortic valves)

The Tricuspid and Mitral Valves are also referred to as "Atrio-ventricular Valves" while the Aortic and Pulmonary Valves are called "Arterial Valves".

The heart in a newborn baby?

In the newborn infant two communications allow blood to pass between the two circuits. The "Ductus Arteriosus" is still open providing a connection between the aorta and the pulmonary artery. In adition the "Foramen Ovale" allows blood to pass between the left and right atriums (LA & RA). Within a few days the ductus closes off completely. The Foramen Ovale closes gradually over several weeks or months, sometimes remaining open as a tiny slit into adolescence or beyond.