Kappagoda, et al (1972) have found that in the dog there exist definite areas at the right atrium and vena cava (and also the left atrium and pulmonary vein) which, if subjected to local pressure with probes, cause a reflex increased in the rate of beating of the SAN. The effect ( in contra-distinction to the usual widespread actions in the sympathetic nervours system) is confine to fibers which terminate at the SAN. If such a reflex exists in man, or can possibly be conditioned by repeated demands impose by AVN rhythm in severe exercise, it would respond to the increased peak atrial pressure by temporarily boosting the SAN. Acting through an approariate delay, this feedback loop could clearly sustain a continuous oscillation. This loop has not been incorporatein the present model, but it has been shown to produce the desired phenomenon on Vit's model. it is hoped that results of thatstudy will be published in the future.