Drugs, cardioplegia and temporary or permanent surgical inter-ruption of conduction pathways mean that sinus bradycardia or heart block requiring pharmacological treatment or pacing is common. A heart rate of 90 is optimal because the ventricle is relatively ‘stiff’ while it recovers from the insult of crossclamping. Infusions of positively chronotropic drugs such as dopamine, dobutamine, isoprenaline or epinephrine can all be used to increase heart rate during this period, which usually lasts about 24 hours. Temporary pacing wires are placed when there is insufficient response to drugs or when the surgery performed carries a high risk of conduction problems (e.g. aortic, mitral valve replacement).