Cardiac arrest is the medical term for when the heart stops beating. It's one of the most terrifying situations a doctor can face. When blood isn’t pumping, all cells start to die from a combination of hypoxia (lack of oxygen), and build up of the normal toxins no longer being cleared. Your organs fail, and death is the ultimate result.

In advanced life support there is a set of concepts called the H’s & T’s, which summarise the reversible causes of cardiac arrest. These are all potentially 'fixable' problems that doctors can treat to save a life. Every second matters when trying to re-start the heart. Seconds can be the difference between complete recovery and permanent disability e.g. through hypoxic brain damage, or amputation of limbs in sepsis.