OBJECTIVES: We investigated the effects of erythropoietin (EPO) on 
neovascularization and cardiac function after myocardial infarction (MI).
BACKGROUND: Erythropoietin exerts antiapoptotic effects and mobilizes 
endothelial progenitor cells (EPCs).
METHODS: We intravenously administered EPO (1,000 IU/kg) immediately [EPO(0) 
group], 6 h [EPO(6h) group], or 1 week [EPO(1wk) group] after the permanent 
ligation of the coronary artery in dogs. Control animals received saline 
immediately after the ligation.
RESULTS: The infarct size 6 h after MI was significantly smaller in the EPO(0) 
group than in the control group (61.5 +/- 6.0% vs. 22.9 +/- 2.2%). One week 
after MI, the circulating CD34-positive mononuclear cell numbers in both the 
EPO(0) and the EPO(6h) groups were significantly higher than in the control 
group. In the ischemic region, the capillary density and myocardial blood flow 4 
weeks after MI was significantly higher in both the EPO(0) and the EPO(6h) 
groups than in the control group. Four weeks after MI, left ventricular (LV) 
ejection fraction in the EPO(6h) (48.6 +/- 1.9%) group was significantly higher 
than that in either the control (41.9 +/- 0.9%) or the EPO(1wk) (42.6 +/- 1.2%) 
group but significantly lower than that in the EPO(0) group (56.1 +/- 2.3%). The 
LV end-diastolic pressure 4 weeks after MI in both the EPO(0) and the EPO(6h) 
groups was significantly lower than either the control or the EPO(1wk) group. 
Hematologic parameters did not differ among the groups.
CONCLUSIONS: In addition to its acute infarct size-limiting effect, EPO enhances 
neovascularization, likely via EPC mobilization, and improves cardiac 
dysfunction in the chronic phase, although it has time-window limitations.