Acute dyspnea is one of the leading clinical symptoms encountered in the emergency room. Its differential diagnosis is wide, ranging from noisy panic attacks to threatening acute heart failure. History taking and physical examination, even when exhaustive are of limited diagnostic value. Patient reported descriptions are fairly correlated to pathophysiology. Vital signs such as the respiratory rate and pulse oximetry carry prognostic significance. Ancillary tests like the chest x-ray lack sensitivity and specificity. The most astonishing adjunct to testing is the chest ultrasound. Its integration into the emergency physician's armamentarium considerably changed clinical management. Fast and accurate, ultrasonography has become the modern era stethoscope. This review discusses acute dyspnea through the main elements useful to diagnosis.