The "heart" represents a person's emotions. This speaks of a person being discouraged as if their emotions were sick. Alternate translation: "Because of this we are discouraged" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-metaphor]])
This means that they have a hard time seeing because they are crying. Alternate translation: "and we can hardly see because our eyes are full of tears" (See: [[rc://en/ta/man/translate/figs-explicit]])