It is not unusual for people with bundle branch block to notice no symptoms, although a test called an EKG (electrocardiogram) can show the abnormal electrical activity that results. This is often the only way that doctors become aware of bundle branch block in their patients. In patients with two diseased bundles, the impulses may be blocked to the extent that no electrical activity reaches the ventricles, and the ventricles must rely on their own electrical activity (idioventricular rhythm), which may be slow enough to cause symptoms such as weakness, lightheadedness, or even fainting.
