The hearts are three types:

1. The correct heart that his secure from all desires that oppose the command of Allah and His prohibitions, and it is secure form all doubts that contradict what he informs. Just as it is secure from worshipping anything else besides Allah and from seeking judgement from any person
other than His messenger.

2. The dead heart, this being the opposite of the correct heart containing no life, neither knowing its Lord nor worshipping Him.

3. The heart that has some life but also has a defect. So it contains love of Allah, faith in Him, sincerity and trust towards Him from those things that are essential to it remaining alive. It also contains the
love of vain desires and preference for them, despicable morals and manners from those things that cause it, and it is continously wavering between these two conditions.

So the first type of heart is the living, humble, soft and gentle heart. The second is the dry, harsh and dead heart. The third is the heart which is diseased, it can either be made secure or have its destruction sealed.

All of the diasease of the heart are founded upon desires and doubts. The life of the heart and its illumination is the cause of all good to be found in it and its death and darkness is the cause of all evil to
be found in it. The heart can never be alive and correct except through cognisance of the truth and loving it and preferring it to everything else. There can never be any happiness or joy or correction for it unless it makes its sole object of worhip and desire Allah alone.

This can never be perfected except through purification of heart,repentance, and its relinquishing itself from all types of false love and despicable manners. This can never be attained except through striving hard against one's soul that incites towards evil, and bringing it to account and combating the satans from among the jinn by holding fast to Allah and knowing their plots and objectives, and safeguaring oneself from them through remembrance of Allah the Exalted and seeking refuge with Him from them. (Ighaatha al Lufhaan of Ibn al-Qayyim and Majmoo' Tataawaa of Ibn Taymiyyah)

The heart becoming defective and weak revolves around two basic matters: the corruption of knowledge and the corruption of intent. These in turn lead to two destructive illnesses-- anger and misguidance. Misguidance being the end result of the corruption of intent. So these two diseases are the lords of all the ailments that afflict the heart. Its cure and lies in guidance based on knowledge. Guidance based on knowledge is to know the truth and to follow it. The whole of the Qur'an is a cure for these two diseases and others and it contains perfect guidance.

Allah said: "He will heal the breast of a believing folk."(9:14)

"And when I become sick, He heals me." (26:80)

"There has come unto you an exhortation from your Lord, a healing for trhat which is in your breasts,a guidance and mercy for the believers." (10:57)

"And We reveal of the Qur'an that which is a healing and a mercy for the believers." (17:82)

"It is a guidance and a healing for those who believe." (41:44)

"There comes forth from their bellies a drink of diverse hues wherein is healing for mankind." (16:69)