OBJECTIVE Dynamic hyperinflation describes the phenomenon of progressive gas trapping that occurs in patients with severe airflow obstruction. It is associated with significant hemodynamic instability and may precipitate cardiac arrest. This report describes a case of hemodynamic collapse secondary to dynamic hyperinflation in a patient during one-lung ventilation. METHODS A 50-yr-old male with a pneumothorax secondary to a ruptured bulla was transferred to the operating room for a left bullectomy. Approximately 30 minutes after initiation of one-lung ventilation in the right lateral decubitus position, sudden ST segment elevation and hypotension occurred, which was refractory to large doses of vasopressor. This culminated in a pulseless electrical activity arrest. The patient was immediately placed supine, disconnected from the ventilator circuit, and resuscitated with chest compressions, fluids, and epinephrine. Auscultation of the right chest revealed no air entry, and needle decompression followed by chest tube insertion in the right chest did not demonstrate any evidence of a pneumothorax. Approximately three to five minutes after the onset of the arrest, the patient's hemodynamics stabilized and there was no evidence of ST elevation. The etiology of the arrest was likely due to dynamic hyperinflation. CONCLUSIONS This report highlights the importance of having a high index of suspicion for dynamic hyperinflation and the key to its treatment: disconnection from the ventilator circuit and cessation of mechanical ventilation to allow the lungs to return to functional residual capacity.