The term "cardiac arrest" indicates that the heart has stopped pumping blood effectively. This is usually due to an abnormal and dangerous electrical pattern in the heart, known as a lethal arrhythmia. Patients with cardiac arrest suddenly lose consciousness, or "pass out." The most common cause of cardiac arrest is ventricular fibrillation (VF), a situation in which the main pumping chambers of the heart, the ventricles, quiver in a disorganized fashion, and are unable to pump blood to vital organs. Another cause of cardiac arrest is ventricular tachycardia (VT), a fast, dangerous rhythm that can stop the hearts pumping ability. A different type of cardiac arrest is known as pulseless electrical activity (PEA), or electromechanical dissociation (EMD). As the name would suggest, PEA is a situation in which an electrocardiogram (EKG) can pick up electrical activity of the heart, yet the heart is not pumping blood. Cardiac arrest due to VF or VT is usually due to cardiac disease, while PEA arrest is not.