If something is terribly sad, it's heart-wrenching. Your best friend might think Romeo and Juliet is ridiculous, but you're not alone if you find the tragic ending absolutely heart-wrenching.
Heart-wrenching is a perfect way to describe something that's so sad it feels like your heart has been permanently damaged — wrenched or twisted by grief. You might also call it "heartbreaking" or "heartrending," words that also attempt to capture a sense of despair or sorrow. A heart-wrenching movie leaves you weeping at the end, and the sudden loss of your wonderful dog is heart-wrenching for the whole family.