The effects of intracoronary arterial injections of nicotine on coronary blood flow, myocardial contractility, cardiac rhythm and the QRS-T complex of the electrocardiogram were studied in intact dogs. The results indicate that nicotine stimulates intrinsic cardiac structures producing parasympathomimetic, sympathomimetic and Bezold-Jarisch reflex responses. The role of these intracardiac receptors is discussed in relation to the circulatory effects resulting from the ingestion of nicotine.