Willamina, could you give some examples of when intestines is used? I find that very interesting.
The heart is an important topic. Often in the church we come to believe that the heart is only evil. Jeremiah 17:9 (see above) is often recited: "The heart is desperately evil and beyond cure, who can know it?" Yet only two translations use the word evil instead of sick.
What happens when we believe our hearts are only evil? We hate them, ignore them, rebuke them - rather than use them. Sick means we need healing, not evisceration. As Zion notes above, we are to pursue purified hearts.