MINAP patient-level data allow the investigation of hospital variation in mortality (in-hospital and 30-day) in a group of unselected patients, taking into account clinical details such as medication use in hospital, as well as features of the hospitals providing care. The proposed study will establish the extent of variation between hospitals in England and Wales, whether this varies by ACS diagnosis, whether the variation has reduced over time and finally which patient-level or hospital-level factors explain any variation found.