['The aim of this study was to evaluate the role of cardiac ultrasound in diagnosing acute heart failure (AHF) in patients with acute dyspnea with available plasma B-type natriuretic peptide (BNP) level.', 'Patients with acute dyspnea presenting to the emergency department (ED) of a tertiary medical center were prospectively enrolled. The enrolled 84 patients received both BNP tests and cardiac ultrasound studies and were classified into AHF and non-heart failure groups.', 'Plasma BNP levels were higher in the AHF group (1236 ± 1123 vs 354 ± 410 pg/mL; P < .001). The AHF group had larger left ventricular end-diastolic dimension (LVEDD; 32 ± 7 vs 27 ± 4 mm/m(2); P < .001) and worse left ventricular ejection fraction (52% ± 18% vs 64% ± 15%; P = .003). Multiple logistic regression analysis showed that both BNP levels more than 100 pg/mL and LVEDD were independent predictors for AHF. In patients with plasma BNP levels within gray zone of 100 to 500 pg/mL, LVEDD was larger in the AHF group than that in the non-heart failure group (29 ± 4 vs 26 ± 4 mm/m(2); P = .044).'] Does cardiac ultrasound help for differentiating the causes of acute dyspnea with available B-type natriuretic peptide tests?