A single high-sensitivity troponin-T (hs-TnT) measurement may be sufficient to risk-stratify emergency department (ED) patients with possible acute coronary syndrome (ACS) using the recalibrated History, Electrocardiogram, Age, Risk Factors, Troponin (rHEART) score. We sought to validate this approach in a multiethnic population of United States patients and investigate gender-specific differences in performance. We conducted a secondary analysis of a prospective cohort study of adult ED patients with possible ACS at a single, urban, academic hospital. We investigated the diagnostic performance of rHEART for the incidence of type-1 acute myocardial infarction (AMI) and other major adverse cardiac events (MACE) at 30 days, using both single (19 ng/L) and gender-specific (14 ng/L for women, 22 ng/L for men) 99th percentile hs-TnT thresholds. The 821 patients included were 54% women, 57% Hispanic, and 26% Black. Overall, 4.6% of patients had MACE, including 2.4% with AMI. Single-threshold rHEART ≤3 had a sensitivity of 94.4% (95% confidence interval 81% to 99%) and negative predictive values of 99.3% (98% to 100%) for MACE; gender-specific thresholds performed nearly identically. Sensitivity and negative predictive values for AMI were 90.0% (67% to 98%) and 99.3% (97% to 100%). Excluding patients presenting <3 hours from symptom onset improved sensitivity for MACE and AMI to 97.0% (84% to 100%) and 94.1% (71% to 100%). Logistic regression demonstrated odds of MACE increased with higher rHEART scores at a similar rate for men and women. In conclusion, a single initial hs-TnT and rHEART score can be used to risk-stratify male and female ED patients with possible ACS, especially when drawn >3 hours after symptom onset.