Introduction - Acute Coronary Syndrome (ACS) is the most common cardiovasculardiagnosis requiring hospital admission worldwide and in the UK. It is associatedwith substantial mortality and healthcare burden. Given the current five dayworking pattern in the UK, we hypothesise a significant variation in the outcomesof patients admitted with ACS during the standard working hours compared without of hours and weekends.Methods: Anonymous data of adult patients aged ≥18 with all types of ACS admittedto 7 hospitals between 2000 and 2013 was obtained and processed usingthe ACALM (Algorithm for Co-morbidity, Associations, Length of stay and Mortality)study protocol. ACALM uses the ICD-10 and OPCS-4 coding systems toidentify patients and the methodology has been used and published widely. Analyseswere performed comparing mortality and length of hospital stay betweenadmissions according to the day of the weeks and core working hours (0900 to1700 Monday to Friday) and out of these hours.Results: Of 929465 adult patient population there were 25294 patients with ACS.Mean age 67 years; Male 64.2%. Over the study period, 38.2% of the patientsdied after ACS during their follow-up period. However, patients admitted on Saturdayor Sunday had significantly higher values of 43.3% and 39.9% respectively.Patients admitted outside of the normal working hours had a value of 39.1% comparedwith 36.5% for patients admitted during working hours. The mean length ofhospital stay (LOS) was significantly higher for patient admitted on Saturday andSunday and outside of core working hours (p<0.05).Table 1. Characteristics of ACS patients according to time of admission to hospitalAll patients Patients admitted Patients admittedduring normal out of normalworking hours working hoursN (%) 25294 (100) 10466 (41.4) 14828 (58.6)Mean Age, years 67 67 66Male, % 64.2 63.9 64.4Number of patients who died duringthe study period (%) 9654 (38.2) 3854 (36.5) 5800 (39.1)*Mean length of hospital stay (days) 7.0 5.9 7.8*Mean survival period, days 1861 1910 1827**Denotes statistical significance, p<0.05.Conclusion: Day and time of hospital admission confer significant variations inoutcomes such as mortality and LOS in patient with ACS. These disparities furtherfuel the argument for 24/7 specialist care in the UK.