While filming The Secret Heart (1946) together, Claudette Colbert and co-star June Allyson became such great friends in real life that Colbert was made godmother to Allyson's daughter Pamela.
Although playing a 17-year old teenager, June Allyson was almost thirty (28) while making this film.
According to an article in The Hollywood Reporter in June 1944 Irene Dunne was originally considered to star in the film before Claudette Colbert was cast.
Chris Matthews (Walter Pidgeon) drives a brand new 1946 Chrysler Town & Country convertible, one of the first post-WWII models off the assembly line. In excellent condition in 2020 this car could be worth over $100,000.
According to information in the American Film Institute Catalog entry for this film Lionel Barrymore replaced Nicholas Joy in the role of Dr. Rossinger and that his scenes were re-shot a month after principal photography had ended.