Progress in both the health sciences and engineering sciences has been necessary for the development of the cardiac pacemaker. From the invention of the vacuum tube triode amplifier in 1906 to that of the oscillator just a few years later; from the early electrocardiograph in 1906 and the first stimulation of a dog's heart in 1927 to the application of electricity to the heart of a stillborn infant only 2 years later, engineering and medicine have progressed together to solve problems in pacemakers. The semiconductor transistor emerged in 1948, and in 1950 work was published on the open heart resuscitation of dogs with voltage pulses to the heart, work whose principle was applied soon after in a human patient with complete heart block. The development of the modern pacemaker has run an exciting course, including such phenomena as one engineer helping to design his own pacemaker. In the past 20 years, science has change the package, the power source, pacing mode, electrodes, and leads of pacemakers; it has improved their reliability and longevity, their programming, telemetry, and instrumentation.