The main cause of sudden cardiac death is the sudden stoppage of the heart, which leads to the loss of blood supply to tissues and organs throughout the body, resulting in necrosis and loss of function of cells, and eventually leading to the failure of multiple organs throughout the body and resulting in death. The causes of sudden cardiac arrest are complex, most often caused by ventricular tachyarrhythmias, i.e. ventricular fibrillation or ventricular tachycardia. Most of these events occur in patients with organic heart disease, especially coronary heart disease, which may not have been previously diagnosed. Patients are at increased risk for these arrhythmic events if they have coronary heart disease or other organic heart disease. In patients with a seemingly normal heart structure, the relatively rare primary arrhythmia syndrome can cause sudden cardiac death. Other conditions, including heart failure, myocarditis, and hypertrophic obstructive cardiomyopathy, can also cause sudden cardiac death. Most patients lose consciousness within seconds to minutes due to lack of cerebral blood flow and usually have no prodromal symptoms. If symptoms do occur, they are nonspecific and include chest discomfort, palpitations, shortness of breath, and weakness.