Abstract: Objective: To study the clinical value of brain natriuretic peptide(BNP) assay in the diagnosis of chronic obstructive pulmonary disease(COPD) complicating with acute dyspnea.Methods: Seventy-eight COPD patients presenting with acute dyspnea were divided into 3 groups:group A contained 43 patients without heart insufficiency,group B 15 patients complicating with left heart insufficiency and group C 20 patients complicating with right heart insufficiency.The plasma BNP levels and ultrasonic cardiogram were measured and compared among the 3 groups;and the BNP cut-off value was determined by the subject performance curve.Results: The BNP level was(60.3±55.8)pg/ml in group A,(1 489.4±1 011.3)pg/ml in group B and(437.9±391.3)pg/ml in group C;the difference was significant among the 3 groups(P<0.01).Echocardiography data showed that the left ventricular inner diameter in group A and group C was significantly less than that in group B;the left ventricular ejection fraction in group A was significantly higher than that in group B and group C(P<0.01),and the left ventricular ejection fraction in group C was significantly higher than that in group B(P<0.01);The internal dimension of the right ventricular and the pulmonary artery pressure in group C were higher than those in group B and group A(P<0.01);The internal dimension of the right ventricle/left ventricle in group B was significantly less than that in group A and group C(P<0.01).The BNP cut-off value was defined as 100 pg/ml by subjects performance curve;the sensitivity of cardiac insufficiency was predicted as 83.5%,and the specificity as 81.5%.Conclusions: The measurement of the plasma BNP level is essential to differential diagnosis of dyspnea etiology in patients with COPD;and the BNP levels are correlated with the type of the heart insufficiency.