Keep your heart with all diligence, for out of it spring the issues of life.
Prov. 4:23
As in water face reflects face, so a man's heart reveals the man. Prov. 27:19
 

A sound heart is life to the body, but envy is rottenness to the bones.
Prov. 14:30
All the days of the afflicted are evil, but he who is of a merry heart has a continual feast.
Prov. 17:15
A merry heart does good like medicine (makes medicine even better) but a broken spirit dries the bones.
Prov. 17:22
There is no peace to the wicked. Is.48:22
As he thinks in his heart, so is he.  
Prov. 23:7