Objective and design: Our prospective observational study is the first study that evaluates the LUS findings of cardiopulmonary interactions in acutely ill children with elevated pro-BNP levels,with the aim of establishing the specific LUS pattern in this category of patients without primary lung diseases.Methodology:We prospectively analyzed epidemiological, clinical, laboratory, instrumental and lung ultrasound parameters in acutely ill children aged 1 month to 18 years admitted to the Department of Pediatrics between March 2020 to August 2020.Among the acutely ill patients evaluated, only patients with pro-BNP> 300 pg / ml and who underwent LUS before the start of any treatment were included. They were stratified into three sub-categories based on the diagnosis A) cardiac disease, B) systemic inflammatory disease / sepsis without functional and / or organic alterations of the myocardium and C) systemic inflammatory disease / sepsis and cardiac disease, and were classified into two groups based on the level of pro-BNP.We also enrolled patients belonging to two other categories (patients with primary infectious lung disease and completely healthy patients) analyzing their epidemiological, clinical, laboratory, instrumental parameters and lung ultrasound findings and comparing them with those of acutely ill children.Results and Conclusion: We found that LUS findings in these acutely ill children are different from the ultrasound pattern of other categories of children and in particular 1) children with acute lower respiratory tract infections and 2) healthy infants.The finding in a child of a sonographic interstitial syndrome with multiple, bright, long, separate and non-confluent B-lines / long vertical artefacts deriving from a normal and regular pleural line, in the absence of subpleural consolidations, is strongly predictive of cardiogenic pulmonary edema or pulmonary congestion in the course of systemic inflammatory disease / sepsis.