In atrial fibrillation and flutter, the atria are stimulated to contract very quickly. This results in ineffective and uncoordinated contraction of the atria. The impulses may be transmitted to the ventricles in an irregular fashion, or only some of the impulses may be transmitted. This causes the ventricles to beat more rapidly than normal, resulting in a rapid or irregular pulse . The ventricles may fail to pump enough blood to meet the needs of the body.
Some cases have no identifiable cause.
Atrial fibrillation or flutter affects about 5 out of 1000 people. It can affect either sex. Atrial fibrillation is very common in the elderly, but it can occur in persons of any age. The pulse may feel rapid or irregular. Blood pressure may be normal or low.