The Four Poisons of the Heart

1) Unnecessary Talking

"Excessive talking without dhikr illah harden the heart & the furthest from Allah are those hard-hearted" 

(Tirmidhi)

2) Unrestricted glances

Between the eye & the heart is an immediate connection. If the glances are corrupted, the heart follows.

Allah commands the believing men that they should lower their gaze

قُل لِّلْمُؤْمِنِينَ يَغُضُّوا مِنْ أَبْصَارِهِمْ 24:30

..

إن الله خبيربما يصنعون

3) Too Much Eating

Consuming small/moderate amounts of food assures tenderness of the heart,

strength of the intellect, humility of the self, weakening of desires. Immoderation brings the opposite qualities

"The human does not fill any vessel that is worse than his stomach".

(Tirmidhi)

4) Keeping Bad Company

"A man follows the religion of his friend; so each one should consider whom he makes his friend"

(Abu Dawud)