Ventricular fibrillation

Illustration showing ventricular fibrillation

In a normal heart rhythm, an electrical signal travels from the heart's upper chambers (atria) to the heart's lower chambers (ventricles), causing the ventricles to contract and pump blood. In ventricular fibrillation, rapid, erratic electrical impulses occur in the ventricles. This causes the ventricles to quiver uselessly instead of pumping blood.