We have developed a pulmonary circulation laboratory exercise that effectively illustrates basic concepts typically taught in a graduate physiology curriculum. The demonstration uses an isolated, perfused rat lung model to delineate the mechanisms by which pulmonary vascular resistance can be altered either passively or in an active manner by contraction or relaxation of vascular smooth muscle. The exercise further offers an opportunity to closely observe an experimental preparation commonly used to study the pulmonary circulation and allows students the opportunity to interpret the resulting physiological data. Student evaluations indicate that the demonstration was received with enthusiasm and provides an effective teaching tool for reinforcing concepts in pulmonary vascular physiology.