When Sissy Spacek was told that she did not have the role in Heart Beat, she broke a glass of wine in her hands. The producer was so impressed by the gesture, that he ultimately gave Spacek the role. He handed her a piece of the shattered wine glass and said, "[that] clinched the deal."
The role of "Ira" is a thinly veiled portrayal of Allen Ginsberg. The name was changed after Ginsberg objected.
The movie is based on the 1976 autobiography "Heart Beat: My Life With Jack and Neal" by Carolyn Cassady. Cassady, who died in 2013 at age 90. Reportedly, she was unhappy with this film version of her book, though she did like Sissy Spacek who played her.
Beat Legend William S. Burroughs visited the set one day, and wrote about it in 'Rolling Stone' magazine, feeling "the past hung in the air" due to the realism in the film. When sitting with Nick Nolte who played Neal, Burroughs "felt Neal sitting there in his cheap 1950s suit with the sleeves pulled up." (source: 'Literary Outlaw - The Life and Times of William S. Burroughs'.)