Earl E. Bakken studied electrical engineering at the University of Minnesota and co-founded Medtronic, a successful medical device company based in Fridley, Minnesota. Bakken created the first external, battery-operated, transistorized, wearable artificial pacemaker. Prior to its invention, pacemakers were large, heavy devices that were carted to the patient and required wall current for power, leaving users vulnerable to power interruptions. Such an outage occurred in 1957, killing a child patient of Dr. C. Walton Lillehei, who promptly asked Bakken to solve this problem. Using a circuit diagram from a metronome, Bakken delivered a battery-powered pacemaker about the size of a deck of playing cards to Lillehei just weeks later. Bakken would further test and refine his invention, although Dr. Lillehei had already put the prototype to successful use, a decision possible only in the days before lengthy FDA approvals of medical devices.