The cardiovascular effects of midazolam 0.2 mg kg-1 i.v. were studied during the induction of anaesthesia in 16 premedicated patients subjected to cardiac surgery. In eight patients with coronary artery disease in whom global resting left ventricular function was normal the haemodynamic changes were small and observations on arterial pressure, cardiac index, stroke index, cardiac filling pressures, systemic and pulmonary vascular resistance appeared to parallel those accompanying deep sleep in healthy volunteers. In eight patients with valvular heart disease and haemodynamic evidence of moderately impaired cardiac performance, pump function during induction with midazolam was maintained, probably as a result of the tendency towards a decrease in systemic vascular resistance. Midazolam appears to be a valuable alternative to conventional induction agents without adverse effects on the cardiovascular system.