Sylvester Stallone's son died from natural causes stemming from a heart condition, medical experts said.
Sage Stallone, 36, died in July from a condition that causes blockage of the arteries. No other factors were involved, the coroner's office in Los Angeles said.
The office said his death had been attributed to natural causes.
Sage was found dead in his home by an employee and a relative on July 13. No foul play had been suspected, and toxicology results showed only a minimal amount of the pain-relieving drug hydrocodone in his system.
Sage Moonblood Stallone was the oldest of Rocky star Sylvester's children and co-starred with his father in two films.
He also became involved in film-making, directing the 2006 short Vic, which was shown at the Palm Springs Film Festival.