We report a case of gas embolism into both right and left circulation in a polytrauma patient with lung contusions, revealed by thoracic CT scan showing the heart and aorta filled with gas. It followed a lung inflation with a O2/N2O mixture for about 30 seconds at a pressure of at least 40 cmH2O in order to obtain apnoea for CT scan and to recruit atelectatic territories. The presumed mechanism was the passage of the O2/N2O mixture during the lung inflation manoeuvre out of disrupted airways into torn pulmonary blood vessels and pushed back into the heart chambers. The patient recovered fully. Lung inflation manoeuvre to obtain a prolonged apnoea during CT scan examinations of thorax is contraindicated in case of thorax trauma, as it carries a risk of gas embolism.