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."
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"
Some of the literal English language translations of this film's foreign language titles, according to the "Robert Downey, Jr. Film Guide" website, are: Argentina: El Amor es Eterno (Love is Eternal); Brazil: Morrendo e Aprendendo (Dying and Learning); France: Drôles de fantômes (Funny Ghosts); Germany: Vier Himmlische Freunde (Four Heavenly Friends); Israel: One More Chance for Life (English translation); Italy: Quattro Fantasmi Per Un Sogno (Four Ghosts for a Dream); Japan: When Love is Smiling (English translation); Poland: Serce i Dusze (Heart and Souls); and Spain: Corazones y Almas (Heart and Souls).
The pictured was nominated for ten Academy of Science Fiction, Fantasy and Horror Films (Saturn) Awards, including Best Fantasy Film, and two nominations each for Best Supporting Actor and Actress, but the film only won just the one Saturn Award, for Best Actor - Robert Downey, Jr.
Appearing uncredited as a psychiatric ward patient in this movie was Chloe Webb, who, coincidentally, had also appeared uncredited in another earlier poltergeist picture , as Elaine in Ghostbusters II (1989).
According to website filminamerica.com, the filming location of the coach crash had "the bus dropped from Stockton Street at California down below the tunnel to Stockton at Sacramento. The Ritz Carlton Hotel at 600 Stockton Street" was visible. The IMDb gives the location as "Stockton Tunnel Southern Approach Overhang, Bush Street and Stockton Street, Downtown, San Francisco, California".
This was the first movie that David Paymer was seen in after Mr. Saturday Night (1992), in which he had received an Academy Award nomination for Best Actor in a Supporting Role. The film was also one of two 1993 feature films featuring Paymer. The other being Searching for Bobby Fischer (1993).
In the scene where Milo attempts to steal back the postage stamps, Marco screams at him, "The next time I see you, you're a dead man". Milo was actually dead, during their next encounter, - just that he was in the body of Thomas (which was also the name of the huge dog at Marco's).
Before she dies, Julia is seen waitressing at "The Purple Onion", a real San Francisco club where comedians such as Phyllis Diller and the Smothers Brothers (Dick Smothers and Tom Smothers) performed. When Julia's boyfriend shows up, the comedian on stage is dressed like, and performing one of the monologues of, Bob Newhart, because he is Newhart's son.