Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked.
Most commonly, it refers to a combination of right bundle branch block (RBBB) and either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB).
Some authors consider left bundle branch block (LBBB) to be a technical bifascicular block, since the block occurs above the bifurcation of the left anterior and left posterior fascicles of the left bundle branch.