The overwhelming majority of places where the Bible uses the Hebrew word leb or its Greek equivalent, kardia , it's used metaphorically. And the heart, in this metaphorical usage, has an incredible variety of uses. Hearts can be glad . Hearts can be troubled . Hearts can be fearful , or courageous .
Hearts can fail, melt, tremble, grow hot , grow sick , and do lots of other things.
When we talk in English about the heart, we see it as the seat of feelings and emotions . Even in English, though, our emotions move around a lot. You've also heard people say that their hear was in their shoes, or that their heart fell into their boots. Didn't know it moved around that much. But in the Bible, the heart, the leb, the kardia, is where everything takes place.