Qalb

The Arabic word for heart is Qlab

In Islamic spirituality, Qalb is not just a physical organ that pumps blood but it has a spiritual life. It is within the physical heart that the spiritual heart resides that can sense and perceive the hidden realities of the soul.

Linguistic Meaning of Qalb

To turn a thing upside-down

To be restless or reverse. 

Conflict within Heart:

It is a supernatural organ, which perceives the Transcendent Realities.

• The qalb is caught between the physical world and the spiritual existence
• Torn between the influence of the nafs(ego) and the ruh (spirit).
• The heart is a point of interaction between the physical and spiritual world. 

Normally the heart is veiled & tarnished by sensual impressions and images, caught between passion, desires, and temptations of nafs. If one strives against the temptation of nafs, he/she will be able to achieve victory and access to higher dimensions and hidden realities of the soul. The heart has the ability to comprehend and the inability to reason or understand.

Sadr (breast) is connected with Islam (Sūra 39:23); qalb (heart) is the seat of īmān (faith) (Sūra 49:7; 16:106); fuad (heart) is connected with marifa (gnosis) (Sūra 53:11); and lubb (innermost heart) is the seat of tauhīd (Sūra 3:190).

• According to Imam Jafar, aql, is the barrier between nafs and qalb -- "the barrier which they both cannot transcend" (Sūra 55:20), so that the dark lower instincts cannot jeopardize the heart's purity. Each of these spiritual centers has its own functions.