Ventricular fibrillation (often shortened to VF or V-Fib) is a serious type of irregular heart rhythm or cardiac arrhythmia. This is a Cardiac arrhythmia that requires immediate shocks with a Defibrillator and Cardio Pulmonary Resuscitation (CPR). If it’s not treated immediately, a patient can suffer brain damage or death. "Arrhythmia" means the heart is not beating normally.