The first external pacemaker was built in 1950 by a Canadian electrical engineer John Hopps. These early pacemakers were large, uncomfortable and worn externally. They were plugged into a wall outlet and affected by mains power failures.
The first subcutaneous implantation was made in 1958, by a Swedish team. By 1960 despite early battery problems such pacemakers lasted only a few years. Current pacemakers with nickel cadmium instead of mercury cells last up to 10 years or more.
They are relatively small with a titanium shell, and are implanted subcutaneously in the upper chest wall. The wire (the lead) is passed into a heart chamber via a major vein.
The end of the lead is attached to the heart muscle by a screw like device or a small fish-hook. Whilst the early devices paced continuously, the contemporary pacemakers pace on demand. The leads can be placed in appropriate heart chamber. They can also defibrillate.