Low heart shot... he's dead... he just didn't know it at the time.
You possibly got the bottom of one or both lungs as well, but the "hit" seems a might low for that... but where there's HOPE, there's a possibility.
Regardless, the low heart shot did the "job"... possibly hitting the lower part of the heart and/or cutting one of the major arteries to the heart.
If you got an artery
only, he "bled-out" on-the-run.
There's also a possibility that the arrow hit bone and glanced upwards taking out one or both lungs and possibility even hitting the spine. If he dropped like a sack-of-rocks, you got a spine-hit!!!
Anyway... good shot. Enjoy the venison. Jus' my 2�...
Strength & Honor...
Ron T.
