He suffers from a dangerously fast heartbeat and a few years ago, had a traditional defibrillator implanted. It soon caused a life-threatening infection and had to be removed.
A new defibrillator was then implanted underneath the skin, lower down in his chest. It contains a wire that goes just outside the chest wall and up the sternum- a path that helps reduce the chance of complications.
The new SICD keeps track of the heart. If Merle's beats erratically, it tries to determine if the situation is life-threatening and will shock him.
After a heart to heart with his doctor, Merle heads home without worries or wires.