Bundle branch block (BBB) is a condition in which the electrical impulses traveling through the heart are slowed or blocked completely from traveling along their normal route through the ventricles. The condition tends to produce no symptoms, although a complete heart block can cause a person to feel either faint (syncope) or as if they are going to faint (presyncope). In those circumstances, the heartbeat may be so slow that an artificial pacemaker is advisable, even if the heart is otherwise healthy.

BBB is relatively rare among young people, and among older people, it is usually caused by an underlying heart condition, such as damage to the heart muscle from a heart attack, or it may occur in conjunction with another condition (e.g., heart failure). Therefore, tests will be ordered to find out the cause of the bundle branch block. A treatment plan will be designed based on what those tests find. In many cases, people will not need treatment for BBB.