The 5 H’s : Causes of Cardiac Arrest and How to Treat Them When someone’s heart stops beating, it’s important to quickly figure out why it happened. The 5 H’s are common, treatable causes of cardiac arrest. If doctors and emergency responders can identify the cause fast, they can take the right steps to save a life. The 5 H’s: Metabolic and Physiological Causes These are problems inside the body that can lead to cardiac arrest: 1. Hypoxia (Low Oxygen Levels) • The body needs oxygen to survive. I