Heisen was one of the early scientists who used eugenics to create advanced soldiers. In January of 1972, he convinced a group of investors in New York City to fund his project. He took about 24 boys and 15 girls for his first experiments. Along with Dr. Patel, he chose a one legged boy name Noonien Singh who had pure unadulterated ferocity for DNA resequencing. After Singh got a new leg, Heisen then met with him in September to assure him that he meant no harm to him. He then taught Singh how to unlock all the knowledge in the world.
In December of 1979, Heisen demonstrated his soldiers and Singh's abilities, such as their weapons training and their regenerative powers. Heisen re-captured Khan using a neural inhibitor when he escaped, knowing that he and the other soldiers were not ready for the world yet.
In August of 1985, Heisen was then contacted by Singh to meet with him. There Heisen was given a gift, which were Khan's and the other soldiers neural inhibitors. Heisen was killed by Singh, who crushed his skull with his own hands. (TOS - Khan comic: "Issue 1")