Atrial synchronous pacing has been considered contraindicated in patients with a high degree of atrioventricular block and concomitant ischaemic heart disease. The rationale for this view was a fear of provoking angina pectoris by a rate-dependent increase in myocardial oxygen consumption. As possible problems with atrial synchronous pacing in patients with ischaemic heart disease have not been extensively studied we have examined whether these patients could benefit from this more physiological method of pacing. Thirteen patients with ischaemic heart disease and a high degree of atrioventricular block were supplied with pacemakers, programmable both in reference to the pacing mode (ventricular inhibited (VVI) or atrial synchronous ventricular inhibited (VDD)) and for maximal synchronous rate. The patients were examined with the pacemaker programmed in the VVI and VDD modes. Maximal exercise capacity was determined by means of bicycle ergometry. There was a statistically significant increase in exercise capacity when comparing VVI (67 + 24) with VDD (79 + 25, P less than 0.001) pacing with suitable programming of maximal synchronous rate. No patient experienced increased anginal pain on VDD pacing and all preferred VDD compared to VVI pacing. In conclusion, VDD pacing should not be considered contraindicated in patients with ischaemic heart disease and a high degree of atrioventricular block, and may, on the contrary, contribute to further clinical improvement.