STUDY OBJECTIVE: To determine whether risk stratification in the out-of-hospital setting could identify patients with chest pain who are at low and high risk to avoid admission or aid direct transfer to cardiac centers. METHODS: Paramedics prospectively enrolled patients with suspected acute coronary syndrome without diagnostic ST-segment elevation on the ECG. The History, ECG, Age and Risk Factors (HEAR) score was recorded contemporaneously, and out-of-hospital samples were obtained to measure cardiac Troponin I (cTnI) level on a point-of-care device, to allow calculation of the History, ECG, Age, Risk Factors, and Troponin (HEART) score. HEAR and HEART scores less than or equal to 3 and greater than or equal to 7 were defined as low and high risk for major adverse cardiac events at 30 days. RESULTS: Of 1,054 patients (64 years [SD 15 years]; 42% women), 284 (27%) experienced a major adverse cardiac event at 30 days. The HEAR score was calculated in all patients, with point-of-care cTnI testing available in 357 (34%). A HEAR score less than or equal to 3 identified 32% of patients (334/1,054) as low risk, with a sensitivity of 84.9% (95% confidence interval [CI] 80.7% to 89%), whereas a score greater than or equal to 7 identified just 3% of patients (30/1,054) as high risk, with a specificity of 98.7% (95% CI 97.9% to 99.5%). A point-of-care HEART score less than or equal to 3 identified a similar proportion as low risk (30%), with a sensitivity of 87.0% (95% CI 80.7% to 93.4%), whereas a score greater than or equal to 7 identified 14% as high risk, with a specificity of 94.8% (95% CI 92.0% to 97.5%). CONCLUSION: Paramedics can use the HEAR score to discriminate risk, but even when used in combination with out-of-hospital point-of-care cTnI testing, the HEART score does not safely rule out major adverse cardiac events, and only a small proportion of patients are identified as high risk.