When someone arrives in the accident and emergency (A&E) department with chest pain, it is hard for doctors to tell whether the pain is due to a heart attack. Some patients have to wait in hospital and have two blood tests taken hours apart before a heart attack can be ruled out. Only 1 in 10 of these patients have had a heart attack – most have less serious conditions like heartburn. Ruling out heart attacks faster would reassure patients earlier and reduce their time spent in hospital. A blood test called high-sensitivity troponin may be used to rule out heart attacks using just one blood sample shortly after a patient arrives in the A&E department. This test measures low levels of heart muscle damage in the blood. This study aimed to find out whether this test works in everyday practice.