300 patients, aged ≥18 years presenting to the emergency room (ER) with acute dyspnoe as principal complaint will undergo initial clinical assessment of the likely etiology of dyspnea by the ER physician in charge. The second assessment by the same physician will include results of NT-proBNP according to predefined cutoffs. Final diagnosis ("Gold Standard") will be done by two experienced investigators after patient discharge taking into account the complete medical record except the results of lung ultrasound. Assessment of chest X-ray and lung ultrasound by investigators will be preforemd blinded regarding all other results.