A high proportion of primary percutaneous coronary interventions performed in the setting of acute myocardial infarction, concur with inadequate myocardial perfusion at the microvascular level. This phenomenon, known as "no-reflow" contributes to reperfusion injury, poor prognosis and to unfavorable clinical outcome. In this study, we evaluated the hypothesis that the synthetic 17β-aminoestrogen Prolame, may confer cardioprotection and prevent against no-reflow. In an open-chest model of 30-min ischemia and 90-min reperfusion, male Wistar rats were randomly assigned to different groups: Control, Prolame, Prolame followed by the nitric oxide synthase inhibitor (L-NAME), and 17β-estradiol. Areas of risk, infarct size and no-reflow were determined by planimetry with triphenyltetrazolium chloride and thioflavin-S stains. Structural damage of the vasculature was measured as capillary compression in clarified tissue after intra-atrial injection of Microfil. Hemodynamic function was obtained at the end of stabilization, ischemia and reperfusion; nitric oxide (NO·) content was determined indirectly using the Griess reaction. Activation of the eNOS signaling cascade was determined by western blot. Prolame reduced the infarcted area, decreased the zones of no-reflow and capillary compression by activating the PI3K/Akt/eNOS signaling pathway in correlation with NO· increase. Prolame also activated endothelial cells augmenting NO· production, which was inhibited by ICI182780 (a selective estrogen receptor down-regulator), supporting the notion that the cardioprotective effect of Prolame involves the preservation of endothelium through the activation of estrogen receptor downstream signaling. Our results provide evidence that Prolame has potential therapeutic application in patients with AMI, as it prevents from both vascular and cardiac tissue damage.