This is a multicentric prospective cohort, involving seven Italian EDs (AOU Città della Salute e della Scienza di Torino, “E. Agnelli” General Hospital - Pinerolo, AO Ordine Mauriziano, Turin, Martini Hospital, Turin, AOU San Luigi Gonzaga, Orbassano, Cardinal Massaia Hospital, Asti, and ASO Santa Croce e Carle, Cuneo, all in Piedmont). Neither traumatic nor already invasively ventilated patients presenting to the ED with a principal complaint of shortness of breath were elegible. After initial clinical assessment, emergency physician is asked to indicate the main diagnosis (cardiac or respiratory dyspnea). Then LUS scanning is performed by the same emergency physician and, at this point, a new presumptive diagnosis (iLUS), based on both initial clinical assessment and LUS findings, is recorded. All patients also underwent standard chest radiography (CXR). After discharge, the entire medical records are independently reviewed by two emergency physicians blinded to the LUS results, in order to determine the final diagnosis of patient’s dyspnea (in case of disagreement, a third emergency physician determined final diagnosis).