I recall a NDE/OBE "empirical test" being done by someone, where they basically put objects or writing in a room that the patients wouldn't even be aware of, and definitely unable to read from normal eye height or on the operating table, and while the reports of OBEs didn't change in their accuracy dealing with things the doctors said or did, or events that took place nearby while they were doing it, they hadn't had a single person report the writing that they should have been able to see while not in their bodies.
The brain does crazy stuff while it's oxygen or blood deprived, it's about the equivalent of holding an electron magnet up to a computer and then running the voltage down to a point that can't properly support the CPU and expecting it to work properly.
When you wake up, the subconscious mind fills in the rest of the experience with details picked up visually, since most OBE experiences are based on sound.
As for the whole heaven thing, welp, we'll see when we get there, but I remain so very highly sceptical.