BACKGROUND: Electrocardiograms (ECGs) are essential in identifying the type and location of acute myocardial infarction. In the setting of inferior wall myocardial infarction (IWMI), identification of the right coronary artery (RCA) as the culprit artery is important because of the potential complications associated with its involvement. OBJECTIVES: To evaluate previous ECG criteria used for the identification of RCA involvement and validate them in the Assessment of the Safety and Efficacy of a New Treatment Strategy with Percutaneous Coronary Intervention (ASSENT 4 PCI) cohort; and to develop an improved simplified score to identify RCA involvement. METHODS: ASSENT 4 PCI patients with IWMI (n=710) were included in the present study. A literature review was conducted to identify previously published criteria to detect RCA involvement. Logistic regression was used to develop a new simplified algorithm for identifying RCA involvement. RESULTS: The sensitivities and specificities of six previous ECG criteria were substantially lower when applied to the ASSENT 4 PCI population. A new algorithm found that ST segment depression in leads I, aVL and V6, and ST segment elevation of greater than 1 mm in lead aVF was associated with a higher likelihood of RCA involvement, and any ST segment depression in V1 and V3 was associated with a lower likelihood of RCA involvement. A simplified risk score found a prevalence of RCA involvement of over 90% among patients with scores of greater than two. CONCLUSIONS: The ECG is useful in identifying RCA involvement in IWMI before angiography. Previously published criteria appear to be inadequate, and the simple algorithm presented in the current study may be a useful tool in identifying RCA involvement at the bedside.