A 37-year-old man with atypical chest pain and complete left bundle branch block showed a marked exercise induced septal defect on Tc-99m sestamibi stress testing. A repeat examination at rest the next day revealed complete reversal of the previous septal defect. Coronary angiography two days later showed a normal coronary artery system. Left bundle branch block has been associated with false-positive results of exercise (and more recently, dipyridamole) TI-201 examinations for septal ischemia. The case presented here may be the first reported example of a false positive Tc-99m sestamibi examination for septal ischemia in the presence of left bundle block.