The aim of our study was to determine the diagnostic accuracy of bedside lung ultrasound (bilateral comet-tail sign or multiple vertical B lines, referred to as "lung rockets"), NT-proBNP and clinical assessment in differentiating heart failure (HF)-related acute dyspnea from pulmonary (COPD/asthma)-related acute dyspnea in the prehospital setting (that is, in the field). The gene discussed is NPPB; the disease is hydrops fetalis.