Just as the heart may be described in terms of being alive or dead, it may also be regarded as belonging to one of the three types; these are the healthy heart, the dead heart, and the sick heart.
The Healthy Heart
On the Day of Resurrection, only those who come to Allaah with a healthy heart will be saved. Allaah subhanahu wa ta’ala says:
A servant with a healthy heart must dedicate it to its journey’s end and not base his actions and speech on those of any other person except Allaah’s Messenger salAllaahu alayhi wasallam. He must not give precedence to any other faith or words or deeds over those of Allaah and His Messenger, may Allaah bless him and grant him peace. Allaah says:
“Oh you who believe, do not put yourselves above Allaah and His Messenger, but fear Allaah, for Allaah is Hearing, Knowing.”
The Dead Heart
This is opposite of the healthy heart. It does not know its Lord and does not worship Him as He commands, in the way which He likes, and with which He is pleased. It clings instead to its lusts and desires, even if these are likely to incur Allaah’s displeasure and wrath.
It worships things other than Allaah, and its loves and its hatreds, and its giving and its withholding, arise from its whims, which are of paramount importance to it and preferred above the pleasure of Allaah. Its whims are its imam. Its lust its guide. Its ignorance its leader. Its crude impulses its impetus. It is immersed in its concern with worldly objectives. It is drunk with its own fancies and its love for hasty, fleeting pleasures.
It is called to Allaah and the aakhirah from a distance, but it does not respond to advice, and instead it follows any scheming, cunning shaytaan. Life angers him and pleases him, and passion makes it deaf and blind  to anything except what is evil.
To associate and keep company with the owner of such a heart is to tempt illness: living with him is like taking poison, and befriending him means utter destruction.
The Sick Heart
This is a heart with life in it, as well as illness. The former sustains it at one moment, the latter at another, and it follows whichever one of the two manages to dominate it. It has love for Allaah, faith in Him, sincerity towards Him, and reliance upon Him, and these are what give it life. It also has a craving for lust and pleasure, and prefers them, and strives to experience them. It is full of self-admiration, which can lead to its own destruction. It listens to two callers: one calling it to Allaah and His Prophet salAllaahu alayhi wasallam and the aakhirah and the other calling it to the fleeting pleasures of this world. It responds to whichever one of the two happens to have most influence over it at the time.
The first heart is alive, submitted to Allaah, humble, sensitive and aware; the second is brittle and dead; the third wavers between either its safety or its ruin.
It has been related on the authority of Abu’d-Darda’ that the Messenger of Allaah, may Allaah bless him and grant him peace, said, “Your love for something makes you blind and deaf.”
Abu Dawud, al-Adab, 14/38; Ahmad, al-Musnad, 5/194. The hadîth is classified as hasan.