The use of ultrasonography for the investigation of pneumomediastinum is limited by the presence of air artifacts. Air accumulation in the mediastinum obscures the heart, sometimes leading to misinterpretation as lung tissue. We found that cardiac apical swinging during the heart cycle, however, can create a uniquely characteristic squeezing of mediastinal free air, producing a sonographic B-line that flashes in and out. We named this dynamic finding, the “disco spotlight” sign. This finding may be useful to confirm the diagnosis of pneumomediastinum.