1. The aim of the present experiments was to study in conscious animals the effect of chemical stimulation of cardiac sensory innervation by bradykinin, a physiological substance known to activate both vagal and sympathetic cardiac sensory nerve endings, at doses devoid of systemic haemodynamic effects.
2. In conscious dogs with implanted catheters bradykinin (100 ng/kg) injected into a cannulated branch of the left coronary artery induced significant (P < 0.01, n = 5) reflex increases in mean arterial pressure and heart rate as well as increases in left ventricular pressure, left ventricular dP/dt max. and coronary blood flow.
3. These changes were obtained in the absence of pain reactions.
4. The concept, derived from experiments on anaesthetized animals, that chemical stimulation of the intact sensory supply of the heart always elicits a cardiovascular depressor reflex mediated by cardiac vagal afferents has to be modified, as pressor sympathetic reflexes may occur after an appropriate stimulus to the fully innervated heart of conscious dogs.