Pulmonary-artery catheterization for hemodynamic monitoring has found widespread acceptance since the introduction of the balloon-tipped flow-directed catheter by Swan and Ganz. Transient right bundle-branch block with insertion of the catheter has been reported to occur in patients with acute myocardial infarction. This complication, however, was thought to be extremely rare, since the soft, flexible, balloon-tipped catheters do not carry the same risk of injury to the cardiac conduction system as do conventional cardiac catheters. This report documents a high incidence of right bundle-branch block (RBBB) occurring during Swan-Ganz catheterization of the pulmonary artery in patients with stable coronary-artery disease. The occurrence of the potentially fatal complication of complete heart block (CHB) associated with Swan-Ganz catheterization of two patients with pre-existent left bundle-branch block (LBBB) is also reported.