Openly gay Ron Palillo, who is best known for playing high school student Arnold Dingfelder Horshack on the ABC comedy sitcom Welcome Back, Kotter, has died of a heart attack. He was 63. reported that Palillo's longtime partner Joseph Gramm called for an ambulance at around 4AM Tuesday. Palillo was pronounced dead at the hospital.

The actor, a heavy smoker, reportedly had scheduled a doctor's appointment for Tuesday to see about a bad cough.

Palillo authored two children's books, The Red Wings of Christmas and A Gift for the Contessa, and wrote a full length play, The Lost Boy, which was produced in 2005 in New York. He also appeared in numerous Broadway productions.

In 1992, he told PEOPLE magazine that his work on the stage had helped him overcome a crippling depression.

Palillo lived in Palm Beach Gardens, Florida. For about the last three years, he had been teaching at the G-Star School of the Arts in West Palm Beach, according to