1 The effects of the beta 2-adrenoceptor stimulant, salbutamol, on cardiac metabolism have been studied in conscious mongrel dogs. The potential effects of anaesthesia on the study of cardiac metabolism have been avoided by prior implantation of arterial (A) and coronary sinus (CS) catheters for blood sampling and a central venous catheter for infusion. Extraction of substrates for myocardial energy metabolism (CA-CS) was assessed 3 to 24 days post-operatively. A 100 micrograms bolus of salbutamol was given followed by an infusion of 3 micrograms/min for 1 h. 2 Although heart rate increased significantly from 106 to 165 beats/min, fractional extraction of oxygen tended to fall from 84% to 77%. Thus an increase in coronary blood flow rather than in oxygen extraction must have maintained an oxygen supply commensurate with the salbutamol-induced tachycardia. 3 Neither CA-CS glucose nor fractional glucose extraction altered significantly during salbutamol infusion despite increases in arterial concentration (CA) of glucose and arterial insulin immunoreactivity and a decrease in CA of free fatty acids (FFA). This suggests that an insulin-antagonistic action accompanies the infusion of salbutamol. 4 The fractional extraction of lactate increased during salbutamol infusion. In part, this may have been a reflection of a decreased myocardial extraction of FFA with salbutamol in this model.