He performed the opening and closing songs on the soundtrack of the 1965 Walt Disney film That Darn Cat!. On December 11 he entered Cedars-Sinai Medical Center in Los Angeles for surgery to repair two artificial heart valves he had received in January 1971. He abandoned the project the rights to which were subsequently bought by actor Kevin Spacey along with Darin's son Dodd.
This knowledge of his vulnerability had always spurred him on to exploit his musical talent while still young. These events deeply affected Darin and sent him into a long period of seclusion. The same year he discovered that he had been brought up by his grandparents not his parents and that the girl he thought was his sister was actually his mother.