This case report presents a patient who inadvertently received transve
nous permanent left ventricular pacing through an unexpected atrial se
ptal defect. This lead malpositioning was proved by two-dimensional an
d transesophageal echocardiography. The abnormal pattern of electric a
ctivation was demonstrated by radionuclide phase image analysis. He ha
s been followed up for a total of forty-three months with antiplatelet
therapy and has been free from systemic embolic phenomena. A simple a
nd readily available method that could lead to early recognition of le
ad malpositioning is reiterated and the various causes, methods of det
ection, and prognosis of left ventricular pacing are discussed.