Heart block occurs when the electrical signals get blocked while trying to go from the atria down to the ventricles. Usually a backup rhythm arises in the ventricles below where the electrical signals are blocked. However, atria and ventricle will fail to work together to pump blood effectively.
Also, the backup rhythm can be inconsistent and unreliable, which ultimately may fail. This can be life-threatening. Depending on the severity of the heart block, a pacemaker may be required.