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Cardiac output is the volume of blood pumped per minute and is calculated as heart rate multiplied by stroke volume. Stroke volume changes with preload, contractility, and afterload; ejection fraction and methods such as the Fick principle provide ways to assess cardiac function. At steady state, venous return equals cardiac output. Its relationship to mean systemic filling pressure, right atrial pressure, and resistance to venous return helps explain how blood volume and venous tone affect flow. The lesson also uses cardiac output and venous return curves to connect shifts in cardiac function or vascular conditions with changes in equilibrium pressure and output, including responses to exercise and sympathetic activation.