Twenty-two patients underwent aortic valve replacement for acquired valvular heart disease with the porcine heterograft prosthesis. In the immediate postoperative period, a transient decrease in the cardiac index (CI) (preoperative 3.0 +/- 0.14 to 2.45 +/- 0.16 L. per minute per square meter, p less than 0.05) and an increase in the systemic vascular resistance (SVR) (preoperative 1,078 +/- 62 to 1,287 +/- 103) dynes/sec./cm.-5, p greater 0.05) were seen; these values returned to preoperative levels by the first postoperative day. After valve replacement, an elevation in the heart rate (HR) (preoperative 75 +/- 2 to 87 +/- 4 beats per minute, p less than 0.05) and a reduction in the stroke volume (SV) and stroke work index (SWI) (preoperative 35 +/- 2 to 26 +/- 2 Gm.-M. per square meter, p less than 0.05) occurred which persisted throughout the study. The endocardial viability ration (EVR) increased after valve replacement. These findings suggest that, following aortic valve replacement, (1) an increase HR is the mechanism utilized to maintain cardiac output, (2) subendocardial perfusion is enhanced as indicated by an increase in the EVR, and (3) the hemodynamic alterations following insertion of the porcine heterograft prosthesis are not different from those observed when other valves are placed in similar patient populations.