Coronary and systemic circulations, and contractility and oxygen consumption of the left ventricular myocardium were depressed as arterial enflurane concentration increased in acute experiments with 22 adult mongrel dogs. Uneven transmural blood flow in the left ventricular free wall did not appear and the inner/outer ratio remained near 1.0 until a very deep stage of the anesthesia was attained and as far as diastolic aortic pressure was maintained above 40 mmHg, according to the microsphere injection study. Once diastolic pressure fell below 35--40 mmHg, the ratios started to be reduced significantly. When arterial enflurane content reached 53.0 +/- 2.1 mg/100 ml (mean +/- s.e.), the ratio became 0.84 +/- 0.08 (p less than 0.001), and simultaneously calculated DPTI/TTI ratio also showed a significant redution from the control (0.79 +/- 0.03, p less than 0.001). The I/O and DPTI/TTI ratios, however, did not correlate significantly with each other until very deep enflurane anesthesia was attained. The lower limit of autoregulation of coronary vascular bed was suggested to be near 35--40 mmHg of diastolic aortic pressure during deep enflurane anesthesia in the dog. Among systolic time intervals measured directly during the study, PEP and ICT showed significant negative correlations with Vmax and LV dp/dt max, while LVET neither changed nor correlated significantly with stroke volume or other parameters representing myocardial contractility during the course of enflurane anesthesia.