United Kingdom emergency departments (EDs) are subject to complex national performance targets and the recent development of Acute Medicine as a subspeciality branch of general medicine that deals solely with the first 12-72 hours of care of the medically unwell patient. The ‘four-hour rule’, introduced in 2003/4, mandated that 98% of patients presenting to an ED must be seen, treated and then admitted or discharged in under four hours. As a result, many EDs have ED-led observation units (OUs). Given that many UK EDs remain relatively understaffed, OUs tend to be small and take very well-defined low-risk patients. Although the St. Thomas Hospital OU offered a high standard of care, its smooth functioning was often challenged by the demands of the four-hour target, with the OU seen as an option to avoid patients ‘breaching’ their ED length of stay target. In 2012, the model of care was changed, with a focus on goal directed outcomes, for both admission and discharge. Eight beds within the new emergency medical unit (EMU) are now dedicated to goal-directed therapy, with the remainder for rapid goal-directed discharge.