Sage Stallone died in July from a condition that causes blockage of the arteries. No other factors were involved.
The coroner's office says Sage's death has been attributed to natural causes.
He 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 hydrocodone in his system.
Sage Moonblood Stallone was the oldest of Sylvester Stallone's children and co-starred with his father in two films. He also became involved in moviemaking, directing the 2006 short "Vic," which screened at the Palm Springs Film Festival.