A series of three horses with classic heaves during crises. Horse 1 exhibits tachypnea, dyspnea, and flared nostrils. Horse 2 has a prolonged expiratory phase of respiration, and a heave line is apparent at end expiration. Horse 3 is undergoing a severe crisis of airway obstruction with tachypnea, expiratory difficulty, abdominal lift, and a heave line.