During a heart attack, clots or narrowed arteries block blood flow, harming or killing cells within the tissue. But the damage doesn't end after the crushing pain subsides. Instead, the heart's walls thin out, the organ becomes enlarged, and scar tissue forms. If nothing is done, the patient can eventually experience heart failure. But scientists now report they have developed gels that, in animal tests, can be injected into the heart to shore up weakened areas and prevent heart failure.