The temporal relationship between left ventricular (LV) shape changes and the development of LV dysfunction, dilation, and sympathoadrenergic hyperactivity was examined in 10 dogs with chronic heart failure produced by multiple sequential intracoronary microembolizations. LV shape was quantitated from serial ventriculograms based on the ratio of the major to minor axis at end systole and end diastole. Measurements were made at baseline (before embolizations) and were repeated at 2, 8, and 16 wk after the last embolization. A significant increase of LV sphericity was present at 2 wk, with only minimal changes occurring thereafter. Despite the tendency for LV shape changes to plateau between 2 and 16 wk, LV ejection fraction continued to decline (31 +/- 1 vs. 20 +/- 2%; P less than 0.001), and LV end-diastolic volume continued to increase (86 +/- 6 vs. 103 +/- 9 ml; P less than 0.01) as did plasma norepinephrine concentration (456 +/- 30 vs. 868 +/- 172 pg/ml; P less than 0.02). These data indicate that in the course of evolving heart failure, LV shape abnormalities precede the development of profound LV dysfunction, dilation, and overt activation of the sympathetic nervous system.