Robert Downey Jr has claimed this one of his favorite films that he has starred in.
Robert Downey, Jr. has said of this film at the "Robert Downey, Jr. Film Guide" website: "Ron Underwood really attracted me to Heart and Souls. It's a character-driven film about sacrifice. The sacrifices people make for one another, and the sacrifice you have to make to find any semblance of bliss, and then there's Thomas, whose head is spinning from the realization that these souls are real, and he's going to have to bend a little to make room for them. Real fine, San Francisco, lots of money. Probably one of the best times in my life. Good movie. It's a fun movie, in which I only have to wear one costume. Even my hair stays the same in the whole movie, and the only thing I had to do was act. So that was a piece of cake."
When Thomas is a kid, not only does he have a picture painted with him and the four ghosts, on his dresser to the left of his bed are four dolls that are representations of each of the ghosts as well.
The guest comedian at The Purple Onion is Bob Newhart, played by his real life son, Robert William Newhart.
Julia's (Kyra Sedgwick's) letter to John (Sean O'Bryan) reads as follows: "John, There was so much I wanted to say to you tonight, but everything I said somehow came out all wrong. I am coming home because I want to be with you. I hope you'll give me another chance. Whatever happens, please know I will love you always. Julia"