The total amount of reflection in the arterial system of the dog is evaluated during control, high, and low peripheral resistance, and an occluded descending aorta. Pressure, as measured in the ascending aorta, may be separated into a (composite) wave travelling from the heart towards the periphery, the forward wave, and a (composite) wave that travels in the opposite direction, the backward wave. This is also true for aortic flow. One may distinguish between reflections at bifurcations of the large vessels and reflections at the arteriolar part of the arterial tree. The former contribute a small, rather constant amount to the returning wave, while the latter reflects a strongly variable amount.