SUMMARY Spontaneously hypertensive male rats (SHR) or normotenslve Kyoto-Wlstar (WKY) male rats underwent either sham or nerve growth factor antiserum (NGFAS) treatment during the first week of life. The NGFAS treatment prevented the development of hypertension in SHR bat did not prevent the development of left ventricular (LV) hypertrophy. At 48 weeks of age, various parameters of LV function were measured In the four treatment groups in vivo under general anesthesia. After the recording of resting parameters, homologous whole blood was transfused until the rise in cardiac output reached a plateau. At rest, LV systolic pressure of the NGFAS-treated SHR was significantly lower than that of the sham-treated SHR and not statistically different from that of the WKY rat. The LV end dlastolic pressures did not differ among the four groups. Both SHR groups had significantly lower cardiac, stroke, and contractility indices than did the WKY groups. Following vascular expansion, LV filling pressure, stroke index, and stroke work index rose in all groups. The response in the SHR was greater than that In WKY groups. Interestingly, the systolic pressure of the NGFAS- treated SHR rose to the same level as in the sham-treated SHR. Heart rate and calculated systemic vascular resistance fell following transfusion. The SHR appears to exhibit an altered response to increased filling pressure and increased afterload. Our findings are consistent with the concept of an alteration in the compliance of the LV in the SHR.