Fatman Scoop passed away after collapsing onstage in Connecticut last month … and, now the medical examiner has revealed his official cause of death.

A rep for the Connecticut M.E.’s office tells TMZ … Scoop — born Isaac Freeman III — passed away from hypertensive and atherosclerotic cardiovascular disease.

We’re told they consider this cause of death to be natural … no foul play suspected.

TMZ broke the story … Scoop collapsed onstage during a performance in Hamden, CT at the end of August — recorded by fans as he hopped up to the turntables before keeling over and falling off the stage.

Paramedics tried reviving the rapper, taking him off the stage on a stretcher and then to the hospital … but, obviously, attempts to revive him were unsuccessful.

FS worked with a ton of notable stars over the years … collabing with the likes of Missy Elliott, Mariah Carey and Jermaine Dupri. He was 56.