Model 3831 cardiac pacemaker, by Devices Ltd, England, 1970-1976

Artificial cardiac pacemakers were developed in the 1960s. They emit regulated electrical impulses. These stimulate the contraction of the heart muscles to provide sufficient rate of heartbeat. A pacemaker is implanted into the chest of a person whose natural pacemaker is too slow or who has a condition where the electrical pulses are impaired. This Model 3831 cardiac pacemaker was made by Devices Limited. It was powered by four mercury-zinc batteries. One million people worldwide are now fitted with pacemakers.