Quite rare and historic piece of biomedical history. Information below is provided by The Smithsonian Museum of American History. They have one of these in their collection donated to them by Medtronic:

In 1958 Earl Bakken an electrical engineer and co-founder of Medtronic Inc. developed the first wearable pacemaker. Bakken named his device the Medtronic 5800 because it was created in 1958. This external pacemaker was originally intended to treat short term heart rate irregularities which sometimes occurred after open heart surgery. It was developed at the request of Dr. Clarence Walton "Walt" Lillehei (1918-1999), a pioneering heart surgeon at the University of Minnesota.

The pacemaker is a simple rectangular white plastic box with two metal handles on each side for attachment to the patient with straps. It is powered by two transistors and a battery. A clear plastic cover protects the two dials (heart rate and the electrical output) recessed into the box and a tiny blinking red light which indicated the device was working. At the top of the pacemaker are two terminals. A wire attached to a terminal was then inserted through the skin and threaded into the heart. The wire sends pluses of electricity to a heart which cannot beat fast enough to pump blood through the body.

Piece is in good condition. Small Bakelite chip in edges where the battery reservoir attaches seen from below. Comes in original case with strap, batteries, manual, and attachment. Also included is a condition report placard that was used to note condition of piece and was last signed and inspected in 1966.