Implantable Cardioverter/Defibrillator. Mine is implanted just over my left pectoral muscle and has two conductive leads (much like the ones kleinbl00 designed) that run to the heart to monitor rhythm and if necessary, deliver corrective electrical impulses to a heart that is misfiring. I'm on my second one. The first one I got when I was 14, was supposed to last until I was 18, and lasted until 19, almost 20. The one I have now is supposed to last well into my 30's which is weird to think about. I've only ever gotten one corrective shock but it saved my life. To answer the inevitable followup question, it hurts. It feels like getting kicked in the chest by a large ungulate. I especially like the tattoo thing because historically my family has been 100% against tattoos, piercings, basically any modification to 'The body Gawd gave you.'