The goal of this study is to evaluate the diagnostic accuracy of lung ultrasound to predict a cardiac origin of dyspnea in unselected patients in the emergency room as compared to standard evaluation. Further goals are to evaluate if lung ultrasound provides additional diagnostic information as compared to clinical examination, NT-proBNP and chest X-ray, to compare the diagnostic accuracy of lung ultrasound in different patient subgroups (heart failure with preserved vs reduced ejection fraction, de novo vs decompensated chronic heart failure, age ≥75 vs <75 years, women vs men and presence vs absence of concomitant pulmonary disease) and to compare demographics and clinical characteristics in different patient populations.