In the Quranic concept, the heart is located in the chest, as Allah described the hearts by saying: 'the hearts within the breasts' (Al-Hajj 46). However, the heart is not limited to the known muscle; the piece of flesh mentioned by the Prophet صلى الله عليه وسلم is only a representation of the heart at the physical level. From divine revelation, starting with this noble ayah, 'Allah has sealed their hearts,' we learn that the heart has a reality beyond its physical dimension, with qualities that can be described, actions attributed to it, things that may be in it, and things that may be on it. People's hearts may resemble one another in good or evil, across time and place. The healthy heart is alive, illuminated, and repentant. However, the diseased heart can become as hard as stone or even harder or be described as sinful, harsh, or in delusion. The heart may experience distress, becoming empty, and on the Day of Judgment, the core of the heart (the 'fu'ad') may become like air in terror—Allah forbid. Hearts may differ and be divided, needing reconciliation to become united. It is also the nature of the heart that Allah has made each human have only one heart, and Allah can come between a human and his heart. Good and evil may come to the heart. The highest level of good occurs when Allah reveals the Quran to the heart of the Prophet صلى الله عليه وسلم and when Allah strengthens the hearts and brings tranquility to them so that faith is realized and steadfastness in jihad is achieved. As for the evil that may afflict the heart, Allah may shield it from good with a covering, a seal, locks, rust, or layers and may seal the heart, as mentioned in this ayah from Surah Al-Baqarah, resulting in complete isolation. Good or evil may enter the heart: Allah may adorn the heart with the beauty of faith, bringing down tranquility, piety, compassion, or mercy into it. On the other hand, the heart may develop a disease such as obsessive love of this worldly life, worship of wealth, or following one's desires. It may harbor hostility toward truth and its people, the worst being obstinate opposition. It may contain avarice, deviation, terror, regret, harshness, severity, hypocrisy, rage, doubt, ignorance, or grudges—may Allah protect us. The heart has actions attributed to it by Allah in the Quran. If we expand our understanding beyond the materialistic limits of secular methodologies using a maqasid (objectives-based) approach, we won't be inclined to interpret the heart's actions as merely 'figurative.' Rather, we believe that the heart is indeed an active organ with willpower, part of human will, even if its actions are not observable or measurable by material tools. These actions include the heart's ability to understand, reason, earn, find tranquility, deviate, undergo trials, believe, sin, listen, tremble, reject, doubt, turn away, deny, neglect, entertain, submit, fluctuate, intend, reach the throat, panic, soften, shudder, repent, humble, incline, be frightened, be hardened, be strengthened, and be blinded. These actions can be good or bad; the heart may earn a good deed or a sin, find tranquility in the remembrance of Allah or in worldly pleasures, soften at the mention of Allah or turn away and shudder, love Allah and good and righteousness, or love desires and evil and corruption, and so forth.