Anencephaly -- A congenital absence of all or most of the brain.

Aorta -- The great arterial trunk that carries oxygenated blood from the heart to be distributed throughout the body by branch arteries.

Atrium -- Either of the two upper chambers of the heart, which receives blood from the veins and forces it into the ventricles (lower chambers).

Congestive heart failure -- Heart failure in which the heart is unable to maintain an adequate circulation of blood in the bodily tissues or to pump out the venous blood returned to it by the veins.

Craniotomy -- A surgical opening of the skull.

Diastole -- The rhythmic relaxation and dilation of the heart chambers, during which time they fill with blood (cf. systole).

Embolism -- The sudden obstruction of a blood vessel by an air bubble, blood clot, or other circulating particles.

Femoral artery -- The main artery of the upper leg.

Hemodynamics -- The branch of physiology that studies the circulation of the blood and the forces involved.

Hypothermia -- Subnormal temperature of the body.

Mitral commissurotomy -- A surgical operation that re-opens the flaps of the mitral valve when they have been partially fused by scarring.

Mitral valve stenosis -- A narrowing of the mitral valve opening caused by partial fusing of the valve flaps. The fusing can occur as a congenital defect or as the result of inflammation and scarring (as in rheumatic fever).

Myocardium -- The middle muscular layer of the heart wall.

Percutaneous -- Effected or performed through the skin.

Pericardium -- The conical, fluid-filled membrane that encloses and protects the heart and the roots of the great blood vessels in vertebrates.

Phrenic nerve -- The nerve that controls the movement of the diaphragm muscle.

Pulmonary arteries -- The arteries that carry deoxygenated blood from the right ventricle of the heart to the lungs.

Rheumatic fever -- An inflammatory disease that sometimes develops after streptococcal infections such as strep throat or scarlet fever. It can affect the heart, joints, skin, and brain, and is responsible for many cases of damaged heart valves. A primary cause of mitral valve stenosis.

Stokes-Adams seizure -- Episodic cardiac arrest and fainting due to failure of the electrical conduction tissue that initiates the heartbeat (heart block).

Systole -- A rhythmically recurrent contraction of the heart by which the blood is forced onward and the circulation is kept up (cf. diastole).

Thoracotomy -- A surgical incision in the chest wall.

Ventricle -- A cavity of a bodily part or organ; in the heart, either of two larger lower chambers that receives blood from a corresponding atrium and from which blood is forced into the arteries. The right ventricle pumps blood back to the lungs to be oxygenated, while the left ventricle pumps oxygenated blood out to the body and to the coronary arteries that supply the heart muscle.