To investigate complementarity and competitiveness between the intrinsic and extrinsic components of the total left ventricular systolic load, hemodynamic data from 18 elderly subjects with severe aortic stenosis were analyzed before and after balloon dilation of the stenosed aortic valve. Multisensor micromanometric pressure measurements allowed calculation (simplified Bernoulli equation) of the ejection velocity and aortic input impedance spectra. Despite a 32% increase in the aortic valve area (from 0.56±0.04 to 0.74±0.05 cm2[mean±SEM],p<0.01), the peak left ventricular systolic pressure fell by only 12% (from 189±10 to 167±8 mm Hg,p<0.01). This was accompanied by an increase in the impedance at the same cardiac output. In a subset of patients (n=9) in whom the peak aortic systolic pressure rose after valvuloplasty (from 115±10 to 128±12 mm Hg,p<0.01), a 40% increase in the aortic valve area was accompanied by a marked increase in the aortic input impedance. In this subset, the steady component of the aortic input impedance increased by 24% (from 960±96 to 1,188±134 dyne.sec/ml,p<0.05), and the characteristic impedance increased by 25% (from 106±13 to 132±19 dyne.sec/ml,p<0.05). Because of an increased aortic impedance acutely following the procedure, the total left ventricular systolic load after balloon dilation of the stenotic valve was only slightly decreased despite a significant increase in aortic valve area. This represents an example of complementarity and competitiveness between the intrinsic and extrinsic components of the total systolic ventricular load. It may explain why improvement in left ventricular performance may be modest acutely following balloon aortic valvuloplasty.