Imam Reza was asked by a follower: “Do Heaven and Hell exist now?”‌

Imam Reza said, “They do, and Prophet Muhammad has seen them in his Ascent.”‌

“Some believe that the Heaven and the Hell have not been created yet,”‌ asked him.

“They are not among us and we are not among them,”‌ said Imam Reza, “Anyone who denies the existence of Heaven and Hell, do not pay attention to the truthfulness of what Prophet Muhammad and we say.”‌

God states in the Qur’an, “They are burning in the fire of the Hell, which they were denying.”‌

Prophet Muhammad also said, “When I was taken to the heavens in the Ascension night, Gabriel took my hand and led me to the Heaven. He gave me a date from Heaven and when I ate it, the light of Fatimah, peace be upon her, was born inside me. Then I went back to the earth, went to Khadijeh and she became pregnant with Fatimah. Fatimah is a heavenly human. Whenever I miss the Heaven, I smell her.”‌

The above quotations assure us that the Heaven and the Hell do exist now.

There are verses in the Qur’an that emphasize on this fact too:

“For indeed he saw him at a second descent, Near the Lote-tree beyond which none may pass: Near it is the Garden of Abode.”‌

God also warns people that the Heaven has already been created for the believers:
“Be quick in the race for forgiveness from your Lord, and for a Garden whose width is that (of the whole) of the heavens and of the earth, prepared for the righteous,-.”‌

And the Hell is waiting for the wrong-doers:

“Fear the Fire, which is repaired for those who reject Faith.”‌

However, we do not know much about the position of Heaven and the Hell. But according to some verses, one can infer that the Heaven is in sublime position;

“And in heaven is your Sustenance, as (also) that which ye are promised.”‌

Source: Tebyan