Here the word "heart" represents the whole person emphasizing one's innermost being. Possible meanings of who cried out are 1) the people of Jerusalem. AT: "The people of Jerusalem shouted to the Lord from their innermost being" or 2) the walls are being personified. AT: "You walls, cry out to the Lord from your innermost being" (See: [[rc://en/ta/man/translate/figs-synecdoche]] and [[rc://en/ta/man/translate/figs-personification]])
The writer speaks to the walls of Jerusalem. He wants the people of Jerusalem to do what he is telling the walls to do. Some translations take this whole section to be spoken to the "walls," though this can be written with the first phrase "walls of the daughter of Zion!" spoken to the "walls," and the rest of the section spoken directly to the people. (See: [[rc://en/ta/man/translate/figs-apostrophe]])
This speaks of the people crying so much that their tears would flow like a river. AT: "Cry many, many tears" (See: [[rc://en/ta/man/translate/figs-metaphor]])