'The Godfather Part III' Actor Anthony Guidera Dead at 65

Actor Anthony Guidera -- known for his roles in "The Godfather Part III" and "Species" -- has died after his heart suddenly stopped, TMZ confirmed.

His wife, Valarie, tells TMZ ... on May 11, the couple was in the living room of their Southern California home when Anthony collapsed, and his heart stopped beating.

Valarie said Anthony was rushed to the hospital, where he was put on life support for 3 weeks. Doctors then took him off life support, per his prior directive, so he could be brought him home for a natural death.

Anthony passed away Saturday ... but his cause of death is still a mystery. Valarie said the doctors have no clue what made Anthony's heart stop.

In 1990, Anthony launched his film career by landing the role of a bodyguard also named Anthony in the third installment of the 'Godfather' trilogy.

Since then, he's played Robbie in the 1995 sci-fi flick, "Species," and received the MTV Movie Award for Best Kiss with his "Species" costar, Natasha Henstridge. 

Anthony also took on smaller movie roles in "The Rock" in 1996, "The Postman" in 1997, and "Armageddon" in 1998.  

In addition, Anthony made appearances in several TV shows, namely "Renegade," "Baywatch," "Angel," and "Star Trek: Deep Space Nine."

Anthony was 65.