The purpose of the present study was to determine the effect of beta-blockade-induced bradycardia and normofrequent ventricular pacing (VP) on regional myocardial (MBF) and cerebral blood flow (CBF) as well as on myocardial oxygen consumption (MVO(2)) using colored microspheres. The MBF at sinus rhythm (SR) was 4.60 +/- 1.27 ml/g/min and decreased to 3.80 +/- 0.74 ml/g/min (p < 0.05) during beta-blockade. The MBF was 5.10 +/- 1.88 ml/g/min during VP with beta-blockade. The endo-/epicardial MBF ratio during VP was significantly reduced. MVO(2) at beta-blockade was significantly lower (0.21 +/- 0.06 ml/g x min(-1), p < 0.05) than at SR (0.47 +/- 0.15 ml/g x min(-1)) and during VP with beta-blockade (0.54 +/- 0.14 ml/g x min(-1)). RESULTS: (i) MBF and MVO(2) are reduced with decreasing mean arterial pressure (MAP) during beta-blockade-induced bradycardia, but MBF and MVO(2) are significantly increased during normofrequent VP with beta-blockade despite a further reduction in MAP. (ii) The MBF ratio is constant during beta-blockade but is significantly lower during normofrequent VP with beta-blockade. (iii) CBF remained constant during all experimental conditions. CONCLUSION: Despite beta-blockade, the subendocardium is jeopardized during normofrequent VP by ischemia.