Quivering or spontaneous muscle contractions especially of the heart is called?

The quivering or spontaneous muscle contractions, especially of the heart, is called fibrillation. Fibrillation is characterized by disorganized and rapid electrical impulses that disrupt the normal coordinated contractions of the heart muscle. This results in ineffective pumping of blood and can lead to a decrease in blood pressure and loss of consciousness if not treated promptly. Fibrillation can occur in both the atria (atrial fibrillation) and ventricles (ventricular fibrillation),