This short chapter focuses on the consequences of diving on the thorax including the changes in hemodynamics and pulmonary mechanics, and the increased respiratory heat loss, both factors playing key roles in the limitation of cardiopulmonary function at depth. The physiological aspects of breath-hold diving will not be commented. The reader will find more information in previous general reviews (Jammes and Roussos, 1995; Jammes et al., 2006). It must be pointed out that all data in humans and experimental animal models were obtained in pressure chambers where individuals were surrounded by gas and not water, the ambient temperature being increased to maintain a relative thermoneutrality. This is never the case in deep sea diving where the water temperature is always below that of the thermoneutral one.