Diagnosing a heart attack quickly is critical: heart attacks kill more than 600,000 people in the United States every year, but if a doctor can accurately and rapidly diagnose a patient, the patient can immediately receive medication or catheter-based treatment. For years, researchers have looked for proteins or biochemicals in the blood that are released when heart cells are injured (biomarkers), but the ones that scientists have identified to date are only detectable several hours after the injury.