1 Rabbit hearts were perfused by the Langendorff technique. The lipid fraction in the perfusate from the heart was isolated and analysed for prostaglandins by thin layer chromatography and quantitative assay on the rat isolated stomach strip.2 Infusion of acetylcholine at a rate of 8 mug/min significantly increased the outflow of prostaglandins from the heart, from 1.8 to 6.2 ng/minute.3 Addition of atropine (1 mug/ml) to the perfusing medium completely abolished not only the mechanical response but also the increase in outflow of prostaglandins caused by infusion of acetylcholine.4 Bilateral stimulation of the parasympathetic nerves to the heart at 5 Hz also significantly increased the outflow of prostaglandins from the organ from 5.2 to 8.3 ng/minute.5 Both prostaglandin E(1) and E(2) were isolated from the lipid fraction of the perfusate.6 The role of prostaglandins in relation to autonomic neurotransmission in the heart is discussed.