Background Usefulness of 64 slice cardiac multi-detector computed tomography (64-MDCT) in acute chest pain has been previously reported. However, triple rule-out protocol of 64-MDCT still needs heart rate control and gives relatively high dose of radiation. Two years ago, 128 slice dual source cardiac CT was introduced and first 128 dual-source MDCT (128-DSCT) came into Korea last year. We developed the clinical practice based on cardiac MDCT in intermediate and low risk patients in emergency department (ED) and introduce the initial experience of 100 cases. Method From November 2009, we developed a chest pain triage protocol based on 128-DSCT in ED. Inclusion criteria was acute chest pain patients with initial presentation within 24 hours before ED visiting. Exclusion criteria was; 1) initially diagnostic ECG for myocardial infarction or positive cardiac enzyme at initial laboratory test, 2) unstable vital sign, 3) history of chronic renal disease, 4) history of allergy to radiocontrast dye, 5) possible for pregnancy and 6) who cannot give consent. DSCT was performed as triple rule-out protocol as soon as possible after initial clinical and laboratory assessment for patients and the result was directly reported to the attending physicians. Initial 100 cases were reviewed and their clinical diagnosis and current status was confirmed by medical record and direct telephone interview. Results Median time for performance of DSCT after ED visit was 190 minutes. Oral beta blocker or sublingual nitroglycerin were applied for 64 patients and average heart rate during DSCT acquisition was 68짹13/minute. Effective radiation dose was 1074.6mGysm. Image quality was excellent in 71% and satisfactory in 15%. Only 1 case was suboptimal for diagnosis. Fifty three patients had insignificant lesion (<25% stenosis) and among them, only one patient was diagnosed as acute coronary syndrome because of vasospasm without fixed lesion (negative predictive value =98%). 26 cases had a coronary artery stenosis more than 50% and among them, 21 patients was finally diagnosed as ACS (positive predictive value =81%) . ACS was finally diagnosed in 23% of study population and aortic dissection or intramural hematoma was diagnosed in 5 patients. There was no case of pulmonary embolism. 75% of the patients were discharged from ED on the basis of clinical presentation and DSCT results and among them, no patients experienced recurrence of chest pain to visit the ED or fatal cardiac events during 3 months after ED visit. Conclusion 128 DSCT is useful in diagnostic accuracy in chest pain triage in ED with high image quality small effective radiation dose.