In Hinduism, the destination is called as Moksha. At the same time, the heaven also there. Are they both same? Normally, Moksha is considered as our spirit mix with God. And heaven is another state of happy life in another world. Can anyone explain the difference between these?
The seven loka in Hindu cosmology are:
Difference between Moksha & Heaven/Swarga:
From wikipedia Heven#Hinduism:
According to Hindu cosmology, above the earthly plane, are other planes: (1) Bhuva Loka, (2) Swarga Loka, meaning Good Kingdom, is the general name for heaven in Hinduism, a heavenly paradise of pleasure, where most of the Hindu Devatas (Deva) reside along with the king of Devas, Indra, and beatified mortals. Some other planes are Mahar Loka, Jana Loka, Tapa Loka and Satya Loka. Since heavenly abodes are also tied to the cycle of birth and death, any dweller of Heaven or Hell will again be recycled to a different plane and in a different form as per the karma and "maya" i.e. the illusion of Samsara. This cycle is broken only by self-realization by the Jivatma. This self-realization is Moksha (Turiya, Kaivalya).
Also refer Svarga:
Svarga is seen as a transitory place for righteous souls who have performed good deeds in their lives but are not yet ready to attain moksha, or elevation to Vaikunta,
I am posting 2 passages from Mahabharata that explain moksha.
Bhishma continued [Suka said],’..By knowledge, one attains to that whither there is no occasion for grief; whither one becomes freed from birth and death; whither one is not subject to decrepitude; whither one transcends the state of conscious existence; whither is Brahma which is Supreme, Unmanifest, immutable, ever-existent, imperceptible, above the reach of pain, immortal, and transcending destruction; whither all become freed from the influence of all pairs of opposites (like pleasure and pain, etc), as also wish or purpose. Reaching that stage, they cast equal eyes on everything, becoming universal friends and devoted to the good of all the creatures.’ Mahabharata Santi Parva Section CCXLI
According to Yudhisthira emancipation is:
There are two well-known paths (for us), viz, the path of the Pitris and the path of the gods. They that perform sacrifices go by the Pitri-path, while they that are for salvation, go by the god-path. By penances, by Brahmacharya, by study (of the Vedas), the great Rishis, casting off their bodies, proceed to regions that are above the power of death. Worldly enjoyments have been styled as bonds. They have also been called action. Liberated from these two sins (viz, bonds and action) one attains to the highest end. ….As a person on the hill-top looketh down upon men on the plain below, so he that has got up on the top of the mansion of knowledge, seeth people grieving for things that do not call for grief. He, however, that is of foolish understanding, does not see this. He who, casting his eyes on visible things, really seeth them, is said to have eyes and understanding. The faculty called understanding is so called because of the knowledge and comprehension it gives of unknown and incomprehensible things. He who is acquainted with the words of persons that are learned, that are of cleansed souls, and that have attained to a state of Brahma, succeeds in obtaining great honours. When one seeth creatures of infinite diversity to be all one and the same to be but diversified emanations from the same essence, one is then said to have attained Brahma. Those who reach this high state of culture attain to that supreme and blissful end, and not they who are without knowledge, or they who are of little and narrow souls, or they who are bereft of understanding, or they who are without penances. Indeed, everything rests on the (cultivated) understanding!’ Mahabharata Santi Parva Section XVII
The 2 passages are describing Advaita style Moksha. This type of Moksha is not the goal of devotees. The lower heavens are great places to stay but have to be vacated when one's Karma is exhausted.
The introduction story of Yoga Vashishta gives answer to your question.
Devadutta and Arishtanemi
Once upon a time there was a king named Arishtanemi. After having performed his kingly duties and having ruled the kingdom with authority, according to the scriptures, he had retired and passed on his kingdom to his son. For hundreds and hundreds of years he had practised severe austerities and meditations in the forest. Lord Indra was so impressed that he sent his messenger Devadutta to invite Arishtanemi to the heavens. So Devadutta went off in a chariot full of the most beautiful damsels and the most learned scholars to invite King Arishtanemi on a first class flight to the heavens.
Devadutta arrived in the forest where Arishtanemi was practising his meditation, and passed on Lord Indra's invitation. Arishtanemi understood that he was being offered a reward for his good deeds, the fruits of his karmas. He said, "Tell me what kind of fruits I will enjoy from these karmas in the heavens?" Devadatta replied, "According to the karmas one has performed in one's life, the quality of the fruit will vary. Due to this variety, there is jealousy amongst the enjoyers of the fruits. Therefore, once the bonus is consumed, you have to go back and pass through another stage of birth."
King Arishtanemi said very firmly, "No, I am not going with you. I am performing these austerities to experience everlasting happiness and peace within, and to know that source, not to go through the same thing. Therefore, I'm not going with you."
Here Arishtanemi got invitation for heaves and he rejected it for the sake of mukthi. Then why these heavens are said to be great in Puranas? In one of his bhashyas Shankara said these explanations of higher lokas are to attain vairagya on them too.
Moksha is final destination an ideal goal for merging with supreme. The heaven and hell are temporary stops and when the good or bad karma get exhausted they return to earth.
trai-vidya mam soma-pah puta-papa yajnair istva svar-gatim prarthayante te punyam asadya surendra-lokam asnanti divyan divi deva-bhogan" (Bhagwat Gita: Chapter Nine verse 20)
"Lord Sri Krishna said: Those who study the Vedas and drink the soma juice, seeking the heavenly planets, worship Me indirectly. Purified of sinful reactions, they take birth on the pious, heavenly planet of Indra, where they enjoy godly delights."
"te tam bhuktva svarga-lokam visalam ksine punye martya-lokam vishanti evam trayi-dharmam anuprapanna gatagatam kama-kama labhante" (Bhagwat Gita: Chapter Nine verse 21)
"Lord Sri Krishna said: When they have thus enjoyed vast heavenly sense pleasures and the results of their pious activities are exhausted, they return to this mortal planet (earth) again. Thus those who seek sense enjoyments by adhering to the principles of the three Vedas achieve only repeated birth and death."
"yanti deva-vrata devan pitrn yanti pitr-vratah bhutani yanti bhutejya yanti mad-yajino ’pi mam" (Bhagwat Gita: Chapter Nine verse 25)
"Lord Sri Krishna said: Those who worship the demigods will take birth among the demigods; those who worship the ancestors go to the ancestors; those who worship ghosts and spirits will take birth among such beings; and those who worship Me (Lord Sri Krishna) will live with Me."
"yat karosi yad asnasi yaj juhosi dadasi yat yat tapasyasi kaunteya tat kurusva mad-arpanam" (Bhagwat Gita: Chapter Nine verse 27)
"Lord Sri Krishna said: Whatever you do, whatever you eat, whatever you offer or give away, and whatever austerities you perform—do that, O Arjuna, as an offering to Me (Lord Sri Krishna)."
"subhasubha-phalair evam moksyase karma-bandhanaih sannyasa-yoga-yuktatma vimukto mam upaisyasi" (Bhagwat Gita: Chapter Nine verse 28)
"Lord Sri Krishna said: In this way you will be freed from bondage to work (karmas) and its auspicious and inauspicious results. With your mind fixed on Me (Lord Sri Krishna) in this principle of renunciation, you will be liberated and come to Me."
So Let's pray to God (Lord Sri Krishna) always in life so that we can go to God's abode than going to heaven as we shall need to take rebirth after going to heaven while we shall get permanent life in God's abode. Let's pray to God always so that He can bless us in this & after this life. Loving & praying to God only can save us from the cycles of birth & death & from all types of miseries in life.