QALB (THE HEART) has two meanings:

The first, a piece of flesh on the left hand side of the chest, which is hollow in the interior, filled with blood and which is again a source of Ruh or life. It is the centre or the mine for the circulation of blood. The detailed description of the heart is to be found in Anatomy. It exists near the chest and appertains to the material world.

The second meaning of Qalb is the soul. It is an immaterial thing or formless Latifa or basic subtle element which has a connection with the material heart. It is just like unseen electricity. It is the principal thing in a man. It catches the knowledge of Allah and the spiritual world. It is punished and rewarded. The connection of the soul with the heart is the connection of attributes with the bodily limbs, or a machine with the machine man, or a house with its inmates.

~ GHAZALI ~