Acute pulmonary thromboembolism is a critical and sometimes fatal event that is difficult for clinicians to diagnose because of its various initial manifestations. Here, we report a previously healthy 50-year-old man without any history of seizures who presented to the emergency ward with the new-onset seizure. Neurology consult was performed, but found no focal neurological deficits. The diagnosis of massive pulmonary embolism was confirmed by echocardiography and pulmonary CT angiography. Alteplase and heparin with therapeutic dosage were started for the patient. After initiating treatment, patient's dyspnea, arterial O2 saturation, and general condition were significantly improved. Echocardiography was repeated and showed a smaller right ventricle size and lower pulmonary artery pressure than the first echocardiography.