Atrial Fibrillation: A disorder of heart rhythm in which the normally regular contractions of the atria of the heart are replaced by rapid and random twitching, resulting in irregular and usually faster than usual contractions of the ventricles.

Palpitations: Awareness of ones own heart beat.

Syncope: Loss of consciousness.

Ventricular Fibrillation: Disorganized, rapid contractions of the muscle of the two ventricles [largest chambers] of the heart, incompatible with life.

Ventricular Tachycardia: Regular heart rate which originates electrically in the ventricles of the heart and which is so abnormally fast that pumping efficiency is severely compromised, causing breathlessness, intolerance of effort, and eventually heart failure.