The power went out in Minneapolis on Halloween in 1957, endangering the lives of open-heart surgery patients who were often attached to a pacemaker. Existing pacemakers were bulky boxes wheeled around on carts and plugged into electrical outlets. Concerned for his patients, a University of Minnesota heart surgeon asked Bakken if he could create a battery-operated pacemaker. Within four weeks, Bakken did just that, and the revolutionary device began saving lives. Hermundslie, an accomplished pilot, flew all over the United States delivering pacemakers to customers. Soon, the “wearable” Medtronic pacemaker was being shipped around the world. One year later, Medtronic produced the first implantable pacemaker.