Nick and Aaron Carter's Father Likely Died of Heart Attack, Family Believes

Nick and Aaron Carter's father complained of chest pains and had twitching in his arm before he went to bed and never woke up ... TMZ has learned.

Sources close to the family tell us ... all signs point to Bob Carter suffering a heart attack when he died Tuesday night. We're told he was working a lot around the house and was out in the hot Florida sun when the chest pains started.

Our sources say the family's grateful everyone was on good terms with Bob.

As we reported ... Nick and Aaron both shared messages about their father's death on Wednesday.