Abstract The response of arterial blood pressure and coronary sinus flow to hemorrhage, to blood transfusion and, in moderately hypovolemic animals, to blood replacement, infusion of physiological saline solution and administration of 50 per cent dextrose solution has been determined. Hemorrhage depresses the blood pressure in about 90 per cent of the animals. It always reduces the coronary sinus flow. Rapid transfusion of blood in normovolemic animals usually brings about a negligible rise in blood pressure and in all animals studied a significant increase in sinus flow. The moderately hypovolemic animal responds to blood replacement, physiologic saline infusion and administration of 50 per cent dextrose solution with a rise in arterial pressure and coronary sinus flow.