Seizure activity causing loss of cardiac output after a Fontan operation.

After a Fontan operation pulmonary blood flow is heavily dependent on respiration. Two patients with a Fontan and normal sinus rhythm developed episodes of collapse with loss of cardiac output secondary to the tonic phase of an epileptic fit. The forced expiratory effort during the tonic phase severely compromised systemic venous return and led to collapse due to loss of cardiac output.