The author studied the effects of circulating catecholamines (CA) on both the left ventricular (LV) contractility index (Emax) and the relationship between LV O(2) consumption (VO(2)) and systolic pressure-volume area (PVA) in 11 excised cross-circulated dog heart preparations. Adrenal medullary stimulation (AMS) of the support dog caused frequencydependent increases in circulating CA. The correlation between the increases in Emax and CA was statistically significant in each heart preparation, but the sensitivity of Emax to CA varied widely. The VO(2)-PVA data point under fixed LV end-diastolic and stroke volumes moved linearly right-upward with increases in Emax. The slope of the VO(2)-PVA locus was steeper than the slope of the reference VO(2)-PVA relationship in control contractility. An infusion of exogenous epinephrine produced similar results to that obtained in the AMS run. The present results indicated a similarity between the effects of endogenous and exognenous catecholamines on both Emax and the elevation of the VO(2)-PVA relation in each heart preparation with a variability in the sensitivity of the elevation of the VO(2)-PVA relationship varied widely among the individual hearts.