Atrial fibrillation is a condition in which the heart beats in an irregular pattern. It is caused by a problem in the heart's electrical pathways. It can be a sign of heart disease or other health problems that affect the heart.
Ventricular fibrillation (V-fib) is a dangerous type of arrhythmia, or irregular heartbeat. It affects your heart’s ventricles. Because sustained V-fib can lead to cardiac arrest and death, it requires immediate medical attention.