What condition does fibrillation refer to in the heart?

Fibrillation refers to a specific condition in the heart characterized by uncontrolled rapid contractions of the heart muscle. This abnormal electrical activity prevents the heart from functioning effectively, leading to inefficient blood pumping. In the case of atrial fibrillation, for instance, the heart's upper chambers (the atria) quiver instead of beating effectively, which can increase the risk of stroke and other complications due to poor blood flow. This is why the correct answer centers on the uncontrolled rapid contractions, as fibrillation disrupts the normal rhythmic beating pattern of the heart.