Competitive breath-hold divers use glossopharyngeal breathing in order to increase their performance. Glossopharyngeal inhalation (GI) increases the volume of air in the lungs above the total lung capacity, thereby increasing the volume of gas available for pressure equalization at great depth. The reverse procedure, glossopharyngeal exhalation (GE), is used to suck air out of the lungs at great depth when the lungs are compressed, thus providing air in the mouth for equalization of pressure in the middle ear. Five Swedish apnea athletes were tested. Their vital capacity (VC) and the volume of air exhaled after GI were measured with a turbine spirometer, while the residual volume (RV), and the volume of gas in the lungs following GE was determined using a helium dilution procedure. Thereafter subjects performed these maneuvers during magnetic resonance imaging (MRI) of the thorax. All subjects exhibited a higher VC + GI (7.8-11.9l) than VC (6.2-9.5l) and lower RV-GE (1.16-1.77l) than RV (1.37-2.40l). MRI revealed pronounced changes in the volume of intrathoracic blood, with a small heart and compressed vessels following GI and the opposite, i.e., enlarged vessels during GE. MRI also showed an invagination of the posterior wall of the trachea, in connection with GE in certain subjects.