An unusual case of life-threatening visceral larva migrans (toxocariasis) is reported herein. The patient was admitted with acute dyspnea and bilateral pleural effusion; rapidly pericardial tamponade developed. Blood and body fluid eosinophilia were elevated. Extensive investigations revealed no malignant process or vasculitis, but Toxocara infection was confirmed by rising specific antibody titers. The high seroprevalence of Toxocara antibodies, particularly in children, suggests that a diagnosis of visceral larva migrans should be considered before a diagnosis of systemic hypereosinophilic syndrome even when clinical presentation is unusual. Prophylaxis against this widespread polymorphic zoonotic infection is desirable in view of the potentially dramatic consequences of infestation.