Regarding the electrical system of the heart, sometimes either the right or the left bundle branch conducts an electrical impulse more slowly than normal, but is not completely blocked. When this occurs, on the side of the slow conduction, the electrical impulse arrives in the ventricle slightly later than normal, but the electrical is not slow enought to be considered a complete bundle branch block. Incomplete bundle branch block sometimes indicates underlying heart disease. But it often has no significance at all. If you have no other signs of underlying heart disease, there is no need for further tests or treatment.