In Islamic thought, the heart (qalb) is considered the core of a person, and is central to their physical, emotional, intellectual, ethical, and spiritual life. The word qalb has multiple interpretations, including: 

• The physical heart: The heart as an organ in the chest cavity that circulates blood 
• The spiritual heart: The heart as the seat of feeling, understanding, and thinking 
• The connection between worlds: The heart as the barzakh, or isthmus, between the visible and invisible worlds, and between the human realm and the realm of the Spirit 
• The seat of faith: The heart as the seat of īmān (faith) 
• The connection to the transcendent: The heart as a connection between individuals and the larger realms of existence 
• The need for protection: The heart as something that needs to be protected from arrogance and spiritual diseases.
• Sufi authors have used Qur’anic terminology to describe different levels of the heart and the human psychospiritual self. For example, some schemas describe the heart as being within the breast (al-ṣadr), which is within the inner heart (al-fū’ād), which is within the innermost heart (al-lubb).