Here we continue from Part 1, where we detailed the workings of the physical heart and the various biological networking of its functions.   The Quran directly links man’s spiritual functions, his purity and health , to his  biological organ called the ‘heart.’

Juxtaposition of the Physical Heart and the Spiritual Heart (Qalb)

The Holy Prophet (ﷺ), in the following Hadith, referred to the heart and its role on health:

“Take heed! In the body there is a piece of flesh which, if it becomes sound and healthy, the whole body becomes sound and healthy, but if it gets spoilt, the whole body gets spoilt, and that is the heart (Qalb).” [Agreed upon, Bukhari and Muslim]

In a literal sense the Hadith applies to the physical heart and its effect on the physical body: when the heart is healthy, the body is healthy, and when it is sick, the entire body suffers.

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An important aspect of this Hadith is that it specifically mentions the word “flesh.”  Flesh is inclusive of the cardiac muscle, and the conductive system of the heart, which is comprized of specialized muscle cells, and not of nerve fibres.

The Hadith may apply to the heart muscle in general —like when the muscles are weak, heart failure ensues and the body is sick, but more importantly any irregularity in the conducting system can cause alteration in the rhythmicity of the heart and severely jeopardize the physical health.

This Hadith was narrated fourteen centuries ago, when knowledge about the heart was more about its spiritual nature rather than about its structure and physiological function.  But the use of the word ‘flesh’ in the Hadith shows that it was predicting the future in the area of the scientific knowledge about this particular organ.  In another version of the Hadith, it refers to the ‘purity of the flesh’:

“In the body is a piece of flesh that, if it is pure, the entire body is pure; and if it is corrupted, the entire body is corrupted. Most surely, it is the Qalb (heart).” [Bukhari and Muslim]

From a medical point of view, there is currently no visible markor detectible chemical impurity about the physical heart to indicate corruption of the mind, soul or spirit.  Thus, when the Prophet refers to the heart’s state of purity , he is referring to the state of spiritual health located in the heart.  In that case, the implication will be, if the spiritual heart is spoilt by impurities like hypocrisy, it will affect the mind and the actions of the body.

 The Spiritual Heart

In the Holy Qur’an, the effects of different kinds of sin on the heart are expressed through use of the words ‘sealing’ (Khatama), ‘covering’ (Akinnah), ‘locking’ (Aqfal), ‘rusting’ (Ran), of the heart, but on visual inspection, there is no such physical effect visible on the physical heart.  These invisible ‘entities’ indicate their metaphysical existence.  Accordingly, their application to the heart indicates the existence of a non-physical dimension of the heart, which is frequently referred to as the Qalb (Spiritual Heart) in the Holy Qur’an.

The Spiritual Heart is a Sensory Organ

  1. The spiritual heart (Qalb) is the receptacle for Divine Revelation, Guidance and Glad Tidings:

“Say: … Gabriel … brings down the (revelation) to thy heart (Qalb) by Allah’s will, a confirmation of what went before, and guidance and glad tidings for those who believe…” [Surah Al-Baqarah, 2:97]

“No kind of calamity can occur, except by the leave of Allah: and if any one believes in Allah, (Allah) guides his heart (Qalb): for Allah knows all things.” [Surah Al-Taghabun, 64:11]

  1. It is the site of Awe, Faith and Trust:

” For, Believers are those who, when Allah is mentioned, feel a tremor in their hearts (qulûb), and when they hear His signs rehearsed, find their faith strengthened, and put (all) their trust in their Lord.” [Surah Al-Anfal, 8:2]

  1. The heart receives warnings:

“Thus have We sent by inspiration to thee an Arabic Qur’an: that you may warn the Mother of Cities [Mecca] and all around her – and warn (them) of the Day of Assembly, of which there is no doubt: (when) some will be in the Garden, and some in the Blazing Fire.” [Surah Al-Shura, 42:7]

  1. It is the site of peace:

“Behold! He (Ibrahim) approached his Lord with a peaceful heart (qalb) . [Surah Al-Saffat, 37:84]

“Those who believe, and whose hearts (qulûb) find satisfaction in the remembrance of Allah: for without doubt in the remembrance of Allah do hearts find satisfaction.” [Surah A-Ra’ad, 13:28]

  1. The heart is the House of Faith:

“The desert Arabs say, “We believe.”  Say [to them, O Muhammad]: “You have no Faith; but you (merely) say: ‘We have submitted our wills to Allah’: for Faith has not yet entered your hearts (qulûb) …”   [Surah Al-Ḥujurât, 49:14]

  1. It receives Guidance:

“Oh Allah! The Controller of the Qulûb, direct our Qulûb to Your Dîn [Prophet’s supplication, Muslim]

The Heart’s Spiritual Faculties Can See, Hear, and Intepret the Message

The physical environment wherein we live is the textbook of spiritual learning.

The spiritual heart (Qalb), residing in the chest, has the ability to spiritualize the visual impulse.  If one fails to spiritualize the visual impulse coming from the environment, then it is blindness, not of the physical eye, but blindness of the spiritual eye:

“Do they not travel through the land, so that their hearts (qulûb) (and minds) may thus learn wisdom and their ears may thus learn to hear? Truly it is not their eyes that are blind, but rather their hearts which are in their breasts.” [Surah Al-Ḥajj, 22:46]

A good example comes from the definition of Isân in the following Prophetic Tradition.  The word Isân (إحسان‎), means “perfection” or “excellence.” That definition comes from the Hadith of Gabriel in which Muhammad (ﷺ) states,

“[Isân is] to worship God as though you see Him, and if you cannot see Him, then indeed He sees you.” (Bukhari and Muslim).

This Hadith indicates one’s level of spirituality: When standing in prayer, we should denounce the material world with ‘Takbîr Tahrîmah’ [the opening Takbîr] and engage our heart in contemplation so that we spiritually connect with Allah ().

History is the witness of the past.  It is incumbant on us to learn lessons from history and to guide ourselves away from the sins that the previous generations committed. They often ignored repeated warnings and faced the consequences of total destruction.  Likewise, we can hear about and see the consequences left by their material ruins, and if we ignore these warning, Allah may choose to put a covering on our eyes and seal our ears.  In view of that, we must open our spiritual faculties of hearing and seeing to avoid similar punishments.

“To those who inherit the earth in succession to its (previous) possessors, is it not a guiding (lesson) that, if We so willed, We could punish them (too) for their sins, and seal up their hearts (qulûb) so that they could not hear?” [Surah Al-A’râf, 7:100]

The Spiritual Heart, its Unique Distinguishing Feature

The human brain and the heart are the distinguishing features of the Khalifah of Allah (). Hearing, seeing and feeling are basic functions of the brain.  The human being has been endowed with the capability for higher perceptions of these sensory impulses so as to create their spiritual counter parts.  Therefore, as a human being, one must not only hear but also listen, not only see but also observe, not only feel but also understand. Thus, it is the joint functions of the brain and the heart to fathom the spiritual message in Allah’s creations:

“Many are the Jinns and men we have made for Hell: They have hearts (qulûb) wherewith they understand not, eyes wherewith they see not, and ears wherewith they hear not. They are like cattle—nay more misguided: for they are heedless (of warning).” [Surah Al-A’râf, 7:179]


Fu’âd is a special attribute of QalbIt is the dwellilng place of Truth, unshakable Faith, Strength and Confidence:

” The (Prophet’s) heart (fu’âd) in no way falsified that which he saw.” [Surah Al-Najm, 53:11]

This verse refers to the Al-Ma’raj (Ascension) of the Prophet (ﷺ).  During this sojourn, he was shown many unknown things and events.  He paid full attention to what he saw and what he saw were all previously unknown to him.  And the next morning he narrated exactly what he saw.  His Fu’âd could not lie about what he saw, but the Quraish in attendance accused him of fabricating what he experienced.  The above verse was revealed to testify to the truth.

Those who repeatedly reject the warning, and ask for Signs only to then reject them, they lose the mercy of Allah for Guidance and finally their faculties become impermeable to the Divine Message:

“And We shall turn [to confusion] their hearts (Af’ida; singular, Fu’âd) and their seeing faculties, just as they refused to believe therein from the first time…” [Surah Al-An’am, 6:110]

“Allah has set a seal (khatama) on their hearts (qulûb); and on their hearing, and on their eyes is a veil; great is the penalty they (incur).” [Surah Al-Baqarah, 2:7]

The Holy Book, the Qur’an, was revealed in stages, over a period of 23 years, to firmly ground the Verses in the Prophet’s heart (Fu’âd), for him to avoid mistakes and to have a clear understanding.  This verse was revealed to answer the non-believers who asked: “Why is not the Qur’an revealed to him all at once?”:

“Thus (it was sent down in parts), that We may strengthen your heart (Fu’âd) thereby, and We have revealed it to you gradually…” [Surah Al-Furqan, 25:32]

adr (pl. udûr)

When translated into English, ‘Sadr’ means the chest; a space bound by the thoracic cage on its sides, the diaphragm below, an outlet guarded by clavicles above, and by the spinal column to its back.  Its contents are the heart, the great blood vessels, the lungs, the esophagus, some lymph nodes and the thoracic ganglia.

Taking a careful look at its ‘construction’ and the structures it surrounds, one  quickly comes to the realization of its importance: the bony cranium protects the brain, the spinal column protects the spinal cord, and now the thoracic cage protects the organs that are at the center of our lives.

In addition, it is also the center of all the secrets of human thoughts and intentions. The chest, or the breast, of a human being is like a ‘cyber space’ where information is kept secret, and no human can reach that information without a pass code.  Allah () —the Creator of the heavens and the earth and whatever is in between— holds the key to that space, knows the human heart and its intention, and has reminded us repeatedly in the Holy Qur’an of His knowledge about our secrecy and plans.  On the day of Judgment, Allah () will look to the heart to judge each by his or her intention:

“And whether you hide your word or publish it, He certainly has (full) knowledge of the secrets of (all) hearts (udûr) . [Surah Al-Mulk, 67:13]

Sadr is also the chamber of Guidance. Allah () “expands the chest” of those who sincerely want to comprehend the Religion of Islam, and He makes it narrow and tight for those tending to deliberately reject His Din.

“And whomever Allah wills to guide, He opens his chest (adr) to Islam; and whomever He wills to leave to their whims, He makes his chest (adr) closed and constricted, as if he is climbing to the sky (to catch his breath)…” [Surah Al-An’âm, 6:125]

It is also the site of treachery, conspiracy and the whispering of the evil ones.  When seeking protection of Allah, one supplicates:

“From the evil of the whisperer who withdraws (from his whispering after one remembers Allah)”, who whispers in the breasts (udûr) of mankind, of Jinn and men.” [Surah Al-Nas, 114: 4-6]


A human being has a body and an inner self. The inner self is a composite of the Ru, the Soul, and the metaphysical aspects of Heart, Mind and BrainThe Ru (Spirit) comes directly from Allah () and confers spiritual qualities to the human being.  The Soul (Nafs), created in pure form, acquires earthly qualities once exposed to the environment, finally having both earthly qualities and spiritual qualities. It is the driving force behind our daily lives: The Soul is the one that responds to our needs and presents to the mind for justification and action. It can be trained to be completely spiritual (  The Mind (‘Aql) is the command center while the brain is the vehicle of execution.

The Heart (Qalb) has both physical and physiological functions, but Fu’âd has only spiritual functions.  It is created pure and it sets the standard of purity for the soul to reflect on.  From a neuroscience point of view, the heart is equipped with all the elements, like that of the brain, to act as a brain (the peripherat brain).  The cranial brain and the ‘cardiac brain’ (the cardiac intrinsic nervous system) complement each other and work synchronously to serve the body. Contrary to common understanding, in the areas of spirituality, the cardiac intrinsic system acts as the receptacle for Divine Inspiration and Guidance.

Fu’ad is a special attribute of Qalb, and adr is the cyber space of secrecy —the details of which are best known to the Creator, Allah ().  Men benefit from all these beautiful non-physical gifts that work harmoniously to make our everyday life complete and comfortable, and they work in concert to open the door for us to return to the Source of Spirituality, our Lord, Allah ():

So whoever hopes for the Meeting with his Lord, let him work righteousness and associate none as partner in the worship of his Lord.”  [Surah Al-Kahf, 18:110]

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Mohammed Siraj Uddin

Mohammed S. Uddin graduated from medical school in 1968 and completed his training in internal medicine and gastroenterology in New York. He taught in medical school and practiced gastroenterology for nearly four decades. He is board certified in Internal Medicine and Gastroenterology. He is a fellow of the Americal College of Gastroenterology and the American College of Physicians.Full BIO

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