The victim and his dog were found in his apartment on the 5300 block of Rising Sun Avenue.
Neighbors say the victim and his brother had only recently found the 8-month-old dog, and it appeared to be malnourished.
A friend allegedly went to check on the man when he saw the dog through a crack in the wall, and the victim not moving.
"The dog was trying to get through the crack," said Tyrone Giddings. "I didn't open the door, cause it wasn't letting me in the door. So I looked through the crack. It's trying to jump through the crack and attack me. It wouldn't let me in the room. So I can't really check no pulse or nothing, but from my stand point, I couldn't see his chest moving."
The 21-year-old victim died at Albert Einstein Medical Center.
Police say autopsy results should help determine what happened.
The dog was taken from the scene by Animal Control.
Comment: Other serious dog attacks of late include the first one listed below which happened in the same city as the one above:
Girl, 7, bitten in face by pit bull in Germantown, Philadelphia
Toddler hospitalized after dog attack in Florida City
Family Dog Shot Dead In Concord After Attack On Toddler