Arteriovenous fistula formation is a known complication of procedures involving major vessels like placement of pacing leads and dialysis catheters. Here we are reporting such an occurrence following temporary and subsequent permanent pacemaker implantation in a case of paroxysmal atrial fibrillation with varying block. Persistent features of congestive heart failure and appearance of a new murmur led us to suspect formation of an arteriovenous fistula. Subsequent angiography revealed a fistulous communication between left vertebral artery and paravertebral venous plexus which drained to a dilated left innominate vein. We thereby recommend a thorough physical examination of such patients who present with features of progressive high output failure or other unexplained symptoms after procedures involving major vessels, to rule out the possibility of an iatrogenic AV fistula..