A lung simulator including a lung bladder, a biasing system providing a relaxed expiration force to the lung bladder with a positive end-expiratory pressure and simulating lung compliance, and a frame holding the lung bladder and biasing member in position. The lung bladder may be inflated and deflated between a positive end-expiratory pressure and a peak inspiratory pressure through the means of a ventilator, a bag mask or mouth to mouth ventilation and may produce a pressure-volume curve similar to that of a lung when the lung bladder is connected to a ventilation source.