The relationship between the extent of preoperative beta-adrenoceptor blockade and the hemodynamic properties of dobutamine was investigated in patients scheduled for elective myocardial revascularization during isoflurane-nitrous oxide anesthesia. Twenty patients had been treated with beta-adrenoceptor blocking drugs for at least 4 weeks before the study; 11 unblocked patients served as control group. The extent of clinical beta-adrenoceptor blockade was quantified using the isoproterenol sensitivity test. The dose of isoproterenol required to increase heart rate by 25 beats/min was defined as the CD25 (chronotropic dose 25), representing the degree of beta-adrenoceptor blockade. Geometric mean CD25/70 kg was 3.8 micrograms in the control group, and 24.5 micrograms in the patients receiving beta-adrenoceptor blocking drugs. The authors found a significant inverse relationship between CD25 values and changes in cardiac index in response to three dobutamine infusion rates (1.0, 2.0, and 4.0 micrograms.kg-1.min-1), the correlation coefficients being -0.78, -0.79, and -0.82, respectively. Compared to unblocked patients, almost no change, or even a decrease, of the cardiac index was observed at higher degrees of clinical beta-adrenoceptor blockade. Moreover, there was a significant linear correlation (r = 0.66 - 0.75) between CD25 values and the effects of dobutamine on systemic vascular resistance index (SVRI), i.e., SVRI decreased in control patients, but increased in patients with high degrees of preoperative beta-adrenoceptor blockade. This unmasked vasocontrictive response to dobutamine was observed despite the fact that the majority of our patients had received cardioselective adrenergic blocking drugs.(ABSTRACT TRUNCATED AT 250 WORDS)