Background: Dyspnea is one of the most frequent complaints in the Emergency Department. Thoracic ultrasound should help to differentiate cardiogenic from non-cardiogenic causes of dyspnea. We evaluated whether the diagnostic accuracy can be improved by adding a point-of-care-ultrasonography (POC-US) to routine exams and if an early use of this technique produces any advantage. Methods: One hundred sixty-eight patients were enrolled and randomized in two groups: Group 1 received an immediate POC-US in addition to routine laboratory and instrumental tests; group 2 received an ultrasound scan within 1 h from the admission to the Emergency Department. The concordance between initial and final diagnosis and the percentage of wrong diagnosis in the two groups were evaluated. Mortality, days of hospitalization in Emergency Medicine department and transfers to other wards were compared. Sensitivity and specificity of the routine protocol and the one including ultrasonography for the diagnosis of the causes of dyspnea were also analyzed. Results: Eighty-eight patients were randomized in group 1 and 80 in group 2. The concordance rate between initial and final diagnoses was significantly different (0.94 in group 1 vs. 0.22 in group 2, p < 0.005). The percentage of wrong initial diagnosis was 5% in group 1 and 50% in group 2 (p < 0.0001). Conclusions: Adding POC-US to routine exams improves the diagnostic accuracy of dyspnea and reduces errors in the Emergency Department.