During the filming of Rocky IV, Sylvester Stallone came dangerously close to dying.

The fourth installment in the Rocky franchise, released in 1985, pitted Stallone’s Rocky Balboa against Dolph Lundgren’s Ivan Drago.

On his YouTube account, the 75-year-old actor has posted The Making of Rocky vs. Drago by Sylvester Stallone, in which he recalls his first day of filming a fight sequence with Dolph Lundgren in the sequel.

During their battle, Stallone suffered an injury that nearly killed him, but it didn’t stop him from including the fight in the final cut of the film.

According to The Expendables actor, he was rushed from a Canadian location to a Californian hospital urgent care unit, where he stayed for four days before returning to finish filming.

After Dolph ‘pulverized’ his heart with a punch, Sly had nuns praying for him in intensive care.

Stallone reveals… in a clip from the Rocky IV documentary

“The first thing we shot [was] my entrance, [Lundgren’s] entrance, and the introductions and then I got really injured during the fight and I had to be flown into intensive care to California from Canada.”

‘In the first round, where he knocked me down, that is for real,’ Sly said, as Dolph exhibited his ‘dominance’ in the situation.

“[Lundgren] pulverised me. And I didn’t feel it in the moment but later that night my heart started to swell. He had bruised the perio cardio sac, which is when the heart hits the chest – like in a car accident when your chest hits the steering wheel.

“My blood pressure went up to 260 and I was going to be talking to angels. Next thing I know I’m on this emergency, low-altitude flight.

“I’m in intensive care surrounded by nuns and then after that, I had to go back and finish the fight.”

Stallone says he spent four days in the intensive care unit before returning to film the movie’s climactic fight. He also disclosed that Lundgren’s chest punch is “what’s in the original movie.”

He stated in the documentary, “How could you take that out?”

Last year he discussed the incident again, saying: ”Dolph Lundgren put me in the hospital for nine days. I knew I was in trouble when I showed up and nuns met you at the ICU.’

He stated that he urged Lundgren to forget about the choreography and “Just go out there and try to clock me. For the first minute of the fight, it is going to be a free-for-all.’

Dolph said in response to the accident: ‘All I did was obey orders. He was the boss. I did what he told me. We came back to L.A. and the producer was like, “Hey Dolph, you’ve got two weeks off — Sly’s in the hospital.”‘

Stallone has had enough to keep him busy in recent months, but he chose to take advantage of the downtime to finish work on a remake of the 1985 film that had been in the works for some time. Ivan Drago, a Soviet boxer, declares his intention to confront Rocky in the ring in the fourth film in the franchise, but instead fights Rocky’s closest friend and former adversary Apollo Creed. When Drago assassinates Creed in the ring, Rocky enters a grudge battle with the Soviet behemoth for the pride of his nation and to revenge Creed’s murder.

In an Instagram post on Tuesday, Stallone encouraged viewers to watch the documentary, adding, “If you haven’t seen this documentary, you should. If you really wanna know what goes on in the filmmakers mind, what really creates the amazing images, and hopefully the excitement …. So watch this documentary, I believe it’s the best one ever done on the subject because you will be there in the moment. #YOUTUBE.COM/SLYSTALLONESHOP.”