Autonomic influences on the heart have been the subject of intense research for many decades but the dramatic expansion in cardiac electrophysiological studies in man has recently renewed clinical interest in autonomic control of the conduction system in health and disease. Unfortunately, most clinical electrophysiological studies still seem to refer to concepts of autonomic nervous control which are clearly out of date. For example in a recent paper, Hluchy and his colleagues referred to “parasympathetic overactivity” in patients with sinus node dysfunction where they used atropine and propranolol to assess autonomic influences on the sinus node [l]. While the use of these two agents is a fairly conventional approach in such clinical electrophysiological studies, it is important that the limits of their inff uence on autonomic neurotransmission arc understood and that other potential neurotransmitters which may be involved in autonomic neural control of the conduction system are recognised. This review describes developments over the past few years in our knowledge of the organisa-