Ventricular fibrillation is an extremely rapid heart rhythm occurring in the lower heart chambers, usually at over 300 beats per minute. In addition to being so very rapid, the electrical activation of the ventricles does not display a specific and repetitive pattern Instead, the electrical signals swirl around the heart in a very chaotic manner. The heart muscle cells are activated without any coordination so that there is no effective heart beat at all. The heart is often described as "quivering" since it does not contract in a meaningful way. As a result, death usually results in 3-5 minutes unless resuscitation is begun.