We studied the effect of correction of anemia with erythropoietin on left ventricular systolic and diastolic function at rest and exercise in 17 chronic hemodialysis patients by means of maximum exercise testing and equilibrium gated radionuclide angiocardiography on three occasions: 1) initial--before erythropoietin administration, 2) intermediate--at the time when the target hemoglobin level reached 100 g/l, and 3) long-term--after 12 months of therapy. After correction of anemia, the patients showed a significant improvement in their response to exercise regarding maximal work load achieved, exercise duration and recovery time. Ejection fraction and peak ejection rate remained unchanged during therapy. At rest, peak filling rate was reduced from 2.62 +/- 1.0 (baseline) to 2.28 +/- 0.9 (intermediate) end-diastolic volume per second, p < 0.01, while no significant difference was observed during exercise. The time to peak filling rate was prolonged significantly during EPO therapy from 157 +/- 30 to 177 +/- 28 ms at rest, p < 0.05, and from 101 +/- 24 to 130 +/- 27 ms during exercise, p < 0.01. By the time of the late study, there were no significant differences between the late and intermediate study. In conclusion, amelioration of anemia with erythropoietin in hemodialysis patients produced improvement in exercise capacity, but diastolic function worsened with therapy and this effect was maintained during the long-term treatment, while systolic function at rest and exercise remained unchanged.