T.K. Carter's Cause of Death Released

T.K. Carter heart gave out ... according to the Los Angeles County medical examiner.

The M.E. lists the actor's cause of death as systolic heart failure. Atrial fibrillation and pulmonary hypertension were contributing factors.

We broke the story ... Carter -- best known for playing Nauls in the 1982 sci-fi horror flick "The Thing" -- was found dead in his Duarte, California residence last week after a call for service was made. No foul play is suspected.

We spoke to T.K.'s brother, Harold, who told us the actor dealt with serious health issues leading up to his untimely passing ... including diabetes and ongoing heart issues.

Law enforcement sources told us the family requested a welfare check on Carter after not hearing from him for several days and informing the police he had high blood pressure. Harold told us T.K. had suffered an apparent head injury before he was found.

Carter appeared in "The Thing," "Space Jam," "The Corner," "The Steve Harvey Show," and other major projects. He was last credited for appearing in three episodes of "The Company You Keep" starring Milo Ventimiglia and Catherine Haena Kim.

Carter was 69.