Observations on the circulatory functions of 4 giraffes are recorded. Both the right and the left heart were catheterized under local anesthesia with a miniature manometer.Cardiac output was determined by employing both indicator dilution method and the Fick principle. Other parameters, such as the circulation time, blood volume, velocity, right and left ventricular pressure ascent as well as the changes in blood pressure occurring with changes in the Posture of the head were recorded. The difficulties of the experiments created certain limitations in their interpretation. The arterial blood pressure is high by human standards and adequate to maintain cerebral perfusion without other means of support. The arterial pressure pulse contour suggests a relatively lax vascular bed with considerable reserve distensibility. Values for cardiac output and blood volume were roughly comparable to those recorded in domestic cattle of the same approximate weight.