Unusual listing I know!! Bought for my husband for after his knee replacement surgery. Thought the combination of massage and TENS would help ease the deep muscle pain around his surgery site. Did not even cross my mind about it being contraindicated with his pacemaker before I ordered it. I AM A NURSE!! Should have crossed my mind!! Anyhow, did not read that fine print until too late to return. Great idea for chronic pain. 2 units and one extra box electrodes. Never opened.