Computed tomography pulmonary angiography (CTPA) is the principal means of evaluating dyspnea in the emergency department. As its use has increased, the number of studies positive for pulmonary embolism (PE) has decreased to less than 20%. Many of the negative PE studies provide an alternative explanation for dyspnea, most commonly pneumonia, pulmonary edema, pleural effusion, or atelectasis. Nonthrombotic emboli may also be suggested. Airway and obstructive lung disease may be detected on CTPA. Pleural and pericardial disease may also explain the dyspnea, but more detailed evaluation of the serosal surfaces may be limited on the arterial phase of a CTPA.