Objective To validate a modified HEART [History, Electrocardiograph (ECG), Age, Risk factors and Troponin] risk score in chest pain patients with suspected non-ST-segment elevation acute coronary syndrome (NSTE-ACS) in the emergency department (ED). Methods This retrospective cohort study used a prospectively acquired database and chest pain patients admitted to the emergency department with suspected NSTE-ACS were enrolled. Data recorded on arrival at the ED were used. The serum sample of high-sensitivity cardiac Troponin I other than conventional cardiac Troponin I used in the HEART risk score was tested. The modified HEART risk score was calculated. The end point was the occurrence of major adverse cardiac events (MACE) defined as a composite of acute myocardial infarction (AMI), percutaneous intervention (PCI), coronary artery bypass graft (CABG), or all-cause death, within three months after initial presentation. Results A total of 1,300 patients were enrolled. A total of 606 patients (46.6%) had a MACE within three months: 205 patients (15.8%) were diagnosed with AMI, 465 patients (35.8%) underwent PCI, and 119 patients (9.2%) underwent CABG. There were 10 (0.8%) deaths. A progressive, significant pattern of increasing event rate was observed as the score increased (P < 0.001 by chi(2) for trend). The area under the receiver operating characteristic curve was 0.84. All patients were classified into three groups: low risk (score 0-2), intermediate risk (score 3-4), and high risk (score 5-10). Event rates were 1.1%, 18.5%, and 67.0%, respectively (P < 0.001). Conclusions The modified HEART risk score was validated in chest pain patients with suspected NSTE-ACS and may complement MACE risk assessment and patients triage in the ED. A prospective study of the score is warranted.