In 1950, Canadian electrical engineer John Hopps  built the first external pacemaker based upon observations by cardio-thoracic surgeons at Toronto General Hospital. With vacuum tube technology, powered by AC from a wall socket, the device posed the potential hazard of electrocution, might produce dangerous ventricular fibrillation and was painful to the patient.

In 1952 a smaller, but still bulky transcutaneous pacing devices was developed using a large rechargeable battery as the power supply.

In 1957, William L. Weirich demonstrated the restoration of heart rate, cardiac output and blood pressure in animals with complete heart block through the use of a myocardial electrode.

In 1958 the Alberto Vejarano Laverde and Jorge Reynolds Pombo constructed a 45kg external pacemaker, powered by a 12 volt car battery and connected to the heart by electrode.

The 1956 invention of the silicon transistor  led to rapid development of practical cardiac pacemaking.