Ron Palillo, actor who played Horshack on 'Welcome Back, Kotter,' dead of heart attack

Ron Palillo (center with hand to his mouth) played Horshack on the popular 1970s sitcom 'Welcome Back Kotter.' (AP)

Ron Palillo, who played Horshack on the hit 1970s sitcom "Welcome Back, Kotter," died Tuesday morning at his home from an apparent heart attack, his rep confirms to FoxNews.com.

TMZ reports that Palillo was found by his partner of many years, Joseph Gramm, around 4:00 am. Gramm called an ambulance, and Palillo was rushed to the hospital, where he was pronounced dead, TMZ reports.

Palillo was 63.

Horshack was known for calling out "Ooh ooh ooh, Mr. Kotter" as one of the Sweathogs on the show, which he starred in along with John Travolta from 1975 to 1979.

Fellow Sweathog actor Robert Hegyes, who played Epstein, died in January at the age of 60.

Travolta and Lawrence Hilton-Jacobs, who played 'Boom Boom' Washington, are the only surviving members of the foursome of misbehaving students.