Levels of heart block are first-degree, second-degree and third-degree heart block. Second-degree heart block is split into two subtypes known as Mobitz I and Mobitz II, according to the National Heart, Lung and Blood Institute. Mobitz I occurs when the electric signal delay with each heartbeat, causing the heart to skip beats. Mobitz II occurs when some of the signals move to the atria and ventricles, while others do not.
Heart block occurs when the electrical signals in the heart affect the way the heart pumps blood, according to Drugs.com. It is diagnosed using electrocardiograpjs, heart monitors, blood tests, chest X-rays and stress tests.
Each level of heart block depends on the severity. First-degree heart block is the least severe, while third-degree heart block is the most severe, according to the National Heart, Lung and Blood Institute. In first-degree heart block, the electrical signals in the heart are slowed as they travel from the atria to the heart's chambers. Second-degree heart block occurs when the signal between the atria and ventricles are slowed to a large degree, preventing the ventricles from contracting and pumping blood. When none of the electrical signals reach the ventricles, it is known as third-degree heart block, possibly resulting in cardiac arrest or death.