 The investigators will prospectively identify all adult 18yrs and older patients presenting to their institutions ED who are being evaluated for ACS and have LBBB on ECG. The investigators will collect data on demographics including age, but not date of birth, cardiac risk factors, date and time of presentation to the ED, ECG measurements, lab and radiographic results cardiac biomarker data including date and time of the sample, stress test results, coronary imaging results, coronary catheterization results and clinical outcomes such as 30-day death or MI. They will collect copies of ECGs and measure the following: STS ratio ratio of the amplitude of ST segment deviation to the S wave amplitude; T-wave morphology entirely discordant, entirely concordant, or biphasic to the PR interval; and standard ST segment deviation. A logistic regression analysis will be used to identify which ECG features are associated with 30-day death, MI, and revascularization. In the sub-cohort of subjects with negative modified Sgarbossa criteria a subanalysis will identify the outcome rates for the following specific sub-populations: those less than 2 consecutive partially-concordant T-wave leads and those with 2 or more consecutive partially-concordant T-wave leads. 