The human heart is a specialized organ in the chest cavity that pumps blood to the tissues. It also receives blood from the tissues to recycle carbon dioxide and oxygen via the lungs. Here is some basic terminology that is used when discussing the human heart.
Oxygenated - Containing oxygen. The heart cycles blood through the body in an attempt to provide oxygen to the cells in the tissues. Blood travels from the heart to the lungs to pick up oxygen and give off carbon dioxide, it is now oxygenated. The blood then goes back to the heart to be pumped out to the tissues. In the tissues, the oxygen is traded for carbon dioxide, making it deoxygenated blood. The deoxygenated blood is then brought to the heart to recycle through the lungs.
Vein - A blood vessel carrying blood from the tissues to the heart. Under normal conditions, the only vein that carries oxygenated blood is the pulmonary vein (going from the lungs to the heart), all others carry deoxygenated blood.
Artery - A blood vessel carrying blood from the heart to the tissues. Under normal conditions, the only artery that carries deoxygenated blood is the pulmonary artery (going from the heart to the lungs), all others carry oxygenated blood. The largest artery is the aorta, the muscular blood vessel attached to the lower left of the heart, forms an arch, and runs down to the abdomen. From the aorta, arterial branches take blood to the head, to the outer portion of the heart, and to the body and extremities.
Vena cava - These are the veins that empty directly into the heart, specifically the right upper chamber. They are known as the superior (upper, or anterior) and inferior (lower, or posterior) vena cava.
Septum - The dividing wall of the heart, separating the chambers with heart tissue. The human heart has 4 chambers, two on each side with a septum between, from base (top) to apex (bottom) in visualizations.
Myocardial - A term meaning "relating to the myocardium". The myocardium is the heart tissue, and the individual cells of the heart are called myocytes. Cardium, cardiac, and coronary are all descriptive terms relating to the heart muscle. Similarly, endocardium means "in the heart", and pericardium means "around the heart".
Coronary arteries - These are the blood vessels responsible for providing the outer myocardium with oxygenated blood.
Ventricle - The larger, lower chambers of the heart. There is a right ventricle, which pumps blood through the pulmonary valve to the lungs via the pulmonary artery, and there is a left ventricle, which pumps blood through the aortic valve to the aorta. The ventricles are separated by the interventricular septum.
Atrium - The upper chambers of the heart. The atria are separated from the ventricles via valves, and from each other by the atrial septum, which joins with the interventricular septum immediately after birth upon the closure of a flap (called the foramen ovale) that allows fetal blood flow to differ from the required blood flow for breathing and oxygenation.
Valve - A one-way flap that prevents the backflow of blood. There are four valves in the heart: the aortic, the pulmonary (also known as semilunar), the tricuspid on the right side, and the mitral (also known as bicuspid) on the left side. Bi- and tri-cuspid refer to the number of tissue flaps that make the valve. The tissue flaps are held taunt by tendons called chordae tendineae, the muscles along the flaps are papillary muslces. Semilunar refers to the shape of the pulmonary valve. Upon ventricle contraction, the valves stay closed to ensure efficient blood flow forward.
Contraction - The mechanical function of the heart muscle is to pump blood, and it does so by contracting, or squeezing. Under normal conditions, the atria contract at the same time, called atrial systole, which pushes blood into the ventricles. The atria begin to relax as the ventricles contract, called ventricular systole, which pushes blood into the lungs or aorta, depending on the side of the heart it is in. The heart then relaxes, called diastole, which is followed by atrial systole to keep the cycle going. During diastole, blood flows into the atria. This two-step systole is part of the well-known "thump thump" of the heartbeat, with the noise actually corresponding to valve closures caused by the contractions.
Node - The involuntary electrical impulses that cause contraction travel through "nodes" in the cardiac tissue. The sinoatrial (SA) node is the natural pacemaker of the heart, initiating systole in the right atrium. The signal travels to the atrioventricular (AV) node in the atrial septum. Other parts of the cardiac electrical conductance system are Purkinje fibers and the bundle of His. The electrical conduction fibers in the heart muscle are modified myocytes with relatively low action potentials for electrical conduction.
Fibrillation - A type of arrhythmia, or an irregular heart rhythm, due to problems in the cardiac nodes, affecting contraction. Atrial fibrillation is estimated to affect more than 2 million Americans, and results in inadequate emptying of the atria. Ventricular fibrillation is more serious and a cause of sudden death.