After World War II Heyde was interned and imprisoned but escaped in 1947. He went underground using the alias Fritz Sawade and continued practicing as a sports physician and psychiatrist in Flensburg. Many friends and associates knew about his real identity, but remained silent even as he was an expert witness in court cases. His true identity was revealed in the course of a private quarrel, and on 11 November 1959 Heyde surrendered to police in Frankfurt after 13 years as a fugitive. Five days before his trial was to start Heyde hanged himself in prison.