Sudden cardiac arrest is the sudden, unexpected loss of heart function, breathing, and consciousness. Sudden cardiac arrest usually results from an electrical disturbance in your heart that disrupts its pumping action, stopping blood flow to the rest of your body. Often it is because the heart is beating too fast and erratically, but sometimes it can result because the heart is beating too slow or not at all.
When the heart stops, the lack of oxygenated blood can cause brain damage in only a few minutes. Death or permanent brain damage can occur within four to six minutes. Time is critical when you're helping an unconscious person who isn't breathing. Take immediate action and call 120, followed by CPR until emergency personnel arrives.