As luck would have it Holter's son was being looked after in Philadelphia, where the surgeons Spitz and Nulsen had already demonstrated that a ventricle-to-atrium diversion system could work. What they needed was an expensive and impractical value that could controle the direction of the flow and maintain the cranial pressure.
A chance discovery showed Holter, after a failed attempt in which a young boy died, that he could use a silicone one-way valve (pressure sealing). After refinement of the silicone and rubber to a medcially suitable grade it was patented and manufactured as Silastic.
Dr. Spitz and John Holter set up a company to manufacture the shunts.
Although he was unable to save his son Casey, his design, the Spitz-Holter valve/shunt has helped millions around the world since the late 1950s.