This review discusses the usefulness of bedside lung ultrasound in the diagnostic distinction between different causes of acute dyspnea in the emergency setting, particularly focusing on differential diagnosis of pulmonary edema and exacerbation of chronic obstructive pulmonary disease (COPD). This is possible using a simple unit and easy-to-acquire technique performed by radiologists and clinicians. Major advantages include bedside availability, absence of radiation, high feasibility and reproducibility, and cost efficiency. The technique is based on analysis of sonographic artifacts instead of direct visualization of pulmonary structures. Artifacts are because of interactions between water-rich structures and air and are called "comet tails" or B lines. When such artifacts are widely detected on anterolateral transthoracic lung scans, we diagnose diffuse alveolar-interstitial syndrome, which is often a sign of acute pulmonary edema. This condition rules out exacerbation of COPD as the main cause of an acute dyspnea.