TEHILIM 17: How do you say in Hebrew “good heart”?

This Mizmor (Psalm) of Tehillim is a “Tefila” (prayer) in which King David asks God to protect him from his enemies. We do not know if those enemies are external enemies, the Pelishtim (Philistines) or other peoples against whom David fought once he was king, or internal enemies, nobles and other men who conspired against David. Perhaps, it may refer to the soldiers of King Saul, who sought to kill David before he was King. If this were the case, we know that in the end, the soldiers stopped from pursuing David because King Shaul had to mobilize his troops to confront the Pelishtim. If this is the case, we would know how and when the “prayer of David” was answered by God.
This Psalm is relatively long, and abounds in metaphors and literary motifs. We will explain only a couple of these metaphors.
David describes with two motifs how he wishes HaShem to protect him from those who persecute him.
Pasuq 8: “Guard me as the pupil of the eye, conceal me under the shadow of Your wings.”
The pupil is the most sensitive part of the eye. And it is protected by the eyelids in a wonderful way. If a foreign object approaches menacingly toward the eye, it is not necessary for the person to make a voluntary movement to protect his eye. The eyelids will close automatically, instantly. David asks God to protect him from his enemies as the eyelids protect the pupil. That is, that even when David does not suspected of being threatened, HaShem would operate its defenses to guard him.
“Conceal me under the shadow of your wings.” In this case, David has Melekh asks God to protect him like the eagle protects its young. Eagles cover their young “fully” with their wings, in a way that perhaps no other animals do (except, perhaps kangaroos). Concealing its chicks from the eyes of their predators. David asks HaShem (and this interpretation is perhaps further evidence that these enemies are the soldiers of King Shaul) to protect him from its enemies, “making him invisible”, in other words, making his enemies not to see him, not discovering him when he hides.
It is also interesting to see how King David describes his enemies.
In Pasuq 10, the King of Israel says: “Fat enclosing [their heart], and their mouths speak vanity.”
The second part of this pasuq (Bible verse) is very clear: the King’s enemies are not humble men, who seek the truth or the good of the people. All they seek is their own benefit. Increase their power to enjoy the reverence of the people. Ultimately, what these individuals want is to satisfy their thirst for honor and their insatiable vanity.
The first part of pasuq, “fat on the heart” requires a less short explanation.
According to Rashi, King David describes his enemies of having “hearts” surrounded by fat. What does it mean?
First, in Hebrew, like in English or Spanish, the heart is the organ related to feelings, especially to sensitivity. When we say about someone that he or she have “a good heart”, we do not mean to say what a cardiologist says when describing one of her healthy patients. Rather, we mean to say that he is a good person.
And yet, there is a curious difference between Hebrew and other languages in terms of motifs used with reference to the heart. For some reason (which I really ignore) in English or Spanish you can describe a good person as someone having a “heart of gold” , i.e.,  very good feelings. In biblical (not modern!) Hebrew, a heart of gold might be an offensive expression. The prophet Yehezqel, for example in pasuq 36:26, speaks of two hearts: a bad hard heart, made of “stone” as oppose to a good and soft heart, made of  “flesh”. I imagine that in the universe of Biblical metaphors, and although not explicitly mentioned by Yehezqel, a “heart of gold”, being that is hard, would be closer to a heart of “stone” than to a heart of “flesh”. In other words, the ideal heart for the Hebrew Bible is not stone or gold, but soft and fleshy.
And yet, there is a further metaphor, indicating that even a heart of flesh sometimes needs repair.
The Tora says in Debarim 10:16 ומלתם את ערלת לבבכם “You should circumcise the foreskin of your heart …”.
What does the circumcision of the heart mean? Our hearts are capable of creating an adipose tissue (“fat” in the metaphor of Tehillim) which is considered as a foreskin of the heart. This additional layer is formed when we lose sensitivity, and we stop feeling uncomfortable in front of injustice, corruption, suffering and other bad things happening around us. A heart surrounded by fat, is a callous heart. That heart,  according to the Tora, must be circumcised. King David describes his enemies with this profound Biblical metaphor. They are people with a heart covered by a “prepuce” (“heartless”, we would say in English), with feelings that are buried under a thick layer of fat, that has grown around it, and they have failed to remove it.