Blood distribution within the ventricle was analysed in acutely prepared turtles Trachemys scripta by measuring the oxygen concentration and flow rates of blood in the central vessels. Pulmonary (Qp) and systemic (Qs) blood flow rates were similar when total cardiac output (Qtot) was below 40 ml min-1 kg-1. Above this value, increments of Qtot were directed to the pulmonary circuit, with Qs levelling off at approximately 20 ml min-1 kg-1. When Qtot was larger than 40 ml min-1 kg-1, the systemic circuit was almost exclusively perfused by left atrial blood and systemic venous return was almost all directed towards the lungs. Blood oxygen levels and flow rates were consistently higher in the right aorta than in the left aorta. Blood movement within the ventricle, coupled with differences in ejection timing, is probably the decisive factor determining this pattern of blood distribution in the turtle heart.

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