A bundle branch block is a heart complication that occurs when the electrical impulses that control heartbeats are delayed, according to Mayo Clinic. An obstruction may block one of the pathways, or bundles, leading to the right or left ventricle, the chambers in the heart.
Electrical impulses travel along the bundle branches in sync, making the left and right heart ventricles contract at the same time, the Texas Heart Institute states. A blocked pathway changes the speed of one of the electrical impulses, causing the heart to contract more slowly. Bundle branch blocks are often related to coronary artery disease, heart valve disease or cardiomyopathy, but individuals may also develop the condition without any symptoms or heart complications.