To assess the hemodynamic effects of acute changes in extracellular ionized calcium concentration, [Ca2+], seven dogs were chronically instrumented to measure heart rate, aortic, left atrial, and left ventricular (LV) pressures, cardiac output, and coronary and renal blood flows. [Ca2+] was lowered 0.35 mmol ± l‐1by citrate infusion and then increased 0.35 mmol ± l‐1above control level by CaCl2infusions. This protocol was performed in the conscious dogs with and without ganglionic blockade (chlorisondamine 2 mg ± kg‐1). LV dP/dtmaxdecreased at low [Ca2+] and increased at high [Ca2+] during all conditions. The other hemodynamic variables measured were only slightly changed by changing [Ca2+] without ganglionic blockade and surprisingly even less with ganglionic blockade. Therefore, the lesser hemodynamic effects induced by acute changes in [Ca2+] in the conscious compared with anesthetized dogs cannot be explained by the depressant effects of the anesthetics upon the autonomic nervous system. We have suggested that the binding of Mg2+to citrate may be of importance for the minor hemodynamic effects in the consci