Heart block is a disease or inherited condition that causes a fault within the heart's natural pacemaker due to some kind of obstruction (or "block") in the electrical conduction system of the heart. Despite the severe-sounding name, heart block may often cause no symptoms at all in some cases, or occasional missed heartbeats in other cases (which can cause lightheadedness, syncope (fainting), and palpitations), or may require an artificial pacemaker to be implanted, depending upon exactly where in the heart conduction is being impaired and how significantly it is affected.