Effective arterial elastance (Ea) and left ventricular end-systolic elastance (Ees) are used as indices of cardiac afterload and cardiac contractility, respectively. We compared the effects of two volatile anesthetics, halothane and isoflurane, on ventriculoarterial coupling using an index of Ea/Ees in 20 mongrel dogs. Ees was obtained using a single-beat estimation technique. Ea was estimated as the ratio of the mean arterial pressure to stroke volume. Basal anesthesia consisted of pentobarbital and alpha-chloralose. Dogs were further anesthetized either with halothane 1 minimum alveolar anesthetic concentration (MAC) and 2 MAC (n = 10) or with isoflurane 1 MAC and 2 MAC (n = 10). Halothane 2 MAC significantly decreased the cardiac output, Ea, and Ees by 35.5% +/- 4.9%, 18.3% +/- 12.6%, and 39.7% +/- 10.8%, respectively. Isoflurane 2 MAC significantly decreased the cardiac output, Ea, and Ees by 37.9% +/- 4.0%, 38.7% +/- 6.4%, and 43.0% +/- 6.0%, respectively. The decreases in cardiac output and Ees were not significantly different between halothane and isoflurane. Halothane increased Ea/Ees from 0.83 +/- 0.05 to 1.22 +/- 0.13, whereas isoflurane maintained the Ees/Es at a constant level. Our results suggest that mechanical efficiency is well maintained during isoflurane anesthesia because it has an equivalent effect on left ventricular contractility and arterial properties, whereas halothane can impair mechanical efficiency by depressing left ventricular contractility more than the arterial system.