I believe heaven begins upon physical death. We step from one reality into another. The soul is separated from the body, but conscious existence continues. I believe heaven is beyond human comprehension and the next life will be more real than this one. Our reward will be based on how we use things and love people. If we love things and use people we will not reap that everlasting reward. When Jesus was on the cross, between 2 thieves, one of them mocked Christ, the other accepted him. Jesus said to the accepting man, "This day you will be with me in Paradise."
Dr. Maurice Rawlings is a physician of internal medicine and he has witnessed many patients that have died and been resuscitated. He wrote a book titled, "Beyond Death's Door." The book features compelling interviews with his patients, on life after life. Dr. Rawlings used to think religion was a bunch of hocus pocus, but he became a believer, after his many emergency room experiences.
I have not experienced Heaven, except in small glimpses in the glory of a sunset over the ocean, the majesty of snow covered mountain peaks and the wonder of the diversity of life that covers this planet we call home. I look forward to that glorious place that is beyond my ability to imagine, because I can imagine a lot.