Purpose: We tried (1) to determine the discriminating ability of lung rockets sign in lung ultrasound and E/Ea (the ratio of peak early diastolic mitral inflow velocity to peak early mitral annular velocity measured by tissue Doppler echocardiography) known as an indicator of pulmonary edema in acute dyspnea and (2) to develop a new algorithm using two variables. Methods: This prospective observational study was performed in an urban emergency department. For the patient with dyspnea at rest, we performed bedside emergency ultrasound assessing the presence of lung rockets sign and measuring the E/Ea. Patients were divided into two groups depending on the cause of dyspnea: pulmonary edema or other cause. We compared the two variables and developed an algorithm using decision tree analysis. Results: A total of 66 patients (39 pulmonary edema, 27 other causes) were enrolled. By univariate analyses, there were significant differences between the two groups in the presence of lung rockets sign (p<0.001) and E/Ea (p<0.001). The area under the receiver operating characteristic curve of the new scoring system with two variables for detecting pulmonary edema was 0.90 (95% CI, 0.801- 0.960). The presence of lung rockets sign and E/Ea > 13.27 had 100% specificity and positive predictive value for pulmonary edema. Conclusion: Lung rockets sign in lung ultrasound and measurement of E/Ea could be helpful in the differential diagnosis of shortness of breath quickly and easily in ED.