Fig. 4. Heart rates of red-eared slider Trachemys scripta in normoxic or anoxic water at 5 and 22°C. The anoxic turtles had been forcefully submerged for 22 days at 5°C and 6 h at 22°C. At this time, the vagal innervation of the heart was blocked by infusion of the cholinergic antagonist atropine, followed by infusion of the ß-adrenergic antagonist nadolol, resulting in a complete autonomic blockade of the heart. [Redrawn from Hicks and Farrell (Hicks and Farrell, 2000b).]