The pattern of pulmonary venous flow was analyzed in an isolated perfused lobe of the dog lung in which a reservoir was substituted for the left atrium. At physiological levels of blood pressure and flow in the pulmonary artery, the pulmonary venous flow was pulsatile and similar in form, magnitude, and transmission time to that observed in intact animals. The amplitude of the pulmonary venous flow pulse was varied in several different ways and the modifications were interpreted on the basis of a simple mechanical analogy. The contour and amplitude of the venous flow pulse is generated predominantly by the right ventricle.