- the formation of fibrils, or fine fibers or filaments.
- uncontrolled twitching or quivering of muscle fibers, such as those of the heart.
- a local and uncontrollable twitching of muscle fibres, esp of the heart, not affecting the entire muscle. Atrial fibrillation results in rapid and irregular heart and pulse rate. In ventricular fibrillation, the heart stops beating
- irregular twitchings of the muscular wall of the heart, often interfering with the normal rhythmic contractions
