This chapter deals with the cardiac system that underpins animal vitality that is more complex than the vegetative one discussed in the previous chapter. The central activity of this system is breathing, and the chapter outlines different types of breathing posited by Galen, the anatomy underpinning them, and his explanation of why the deprivation of breath leads to the loss of life. The chapter also focuses on the three types of pneuma theorized by Galen, discussing their proper activities and properties enabling these activities. The focus on pneuma also brings attention to yet another Galenic division of parts into solids, fluids and pneumata. This division of tissues according to their texture and speed of movement offers an important glimpse into how Galen conceives of interaction between parts. Moreover, the rapid alterations in the pneumatic tissues underpin the physiological understanding of animal vitality.