AIM: To create and validate a simple scoring system for predicting 30-day mortality in patients presenting with acute coronary syndromes (ACS) at their moment of admission. METHODS AND RESULTS: 2407 consecutive patients presenting to Harefield Hospital with measured arterial blood gases, from January 2011 to December 2020, were studied to build the training set. 30-day mortality in this group was 17.2%. A scoring algorithm that was built using binary logistic regression of variables available on admission was then converted to an additive risk score. The resultant scoring system is the BE-ALIVE score, which incorporates the following factors:Base Excess (1 point for <-2 mmol/L), Age (<65 years: 0 points, 65-74: 1 point, 75-84: 2 points, ≥85: 3 points), Lactate (<2 mmol/L: 0 points, 2-4.9: 1 point, 5-9.9: 3 points, ≥10: 6 points), Intubated (2 points), Left Ventricular function (mildly impaired or better: -1 point, moderately impaired: 1 point, severely impaired: 3 points) and External/out of hospital cardiac arrest 2 points).The scoring system was validated using a testing set of 515 patients presenting to Harefield Hospital in 2021. The validation metrics were excellent with a c-statistic of 0.9, Brier's score 0.06 vs a naïve classifier of 0.15, Spiegelhalter's z-statistic probability of 0.267 and a calibration slope of 1.08. CONCLUSION: The BE-ALIVE score is a simple and accurate scoring system to predict 30-day mortality in patients presenting with ACS. Appreciating this mortality risk can allow prompt involvement of appropriate care such as the shock team.