Here the heart represents a person, but specifically his will. Alternate translation: "He humbled them by allowing them to suffer hardship" (See: [[rc://en/ta/man/translate/figs-synecdoche]])
The word "stumbled" refers to times when these people got into very difficult situations. Alternate translation: "they got into trouble and there was no one to help them out of it" (See: [[rc://en/ta/man/translate/figs-explicit]])