Non‐technical summary  The brain controls the heart through parasympathetic (vagal) and sympathetic nerves. Vagal control is integral to cardiac health and a loss of vagal tone is a poor prognostic sign in cardiovascular diseases such as heart failure and hypertension. The vagal drive to the heart is transmitted across synapses located in the cardiac ganglia on the heart. We have developed a novel methodology to make intracellular recordings from cardiac ganglion neurones on the surface of the beating heart in a preparation with intact functional drive from the brainstem. We show how these neurones process their synaptic inputs and demonstrate that the ganglion plays a key role in regulating the level of vagal tone reaching the heart. This identifies the cardiac ganglion as a viable target for interventions to restore the transmission of vagal tone in cardiovascular diseases.