Background. Female sex and advanced age have adverse prognostic meaning in acute myocardial infarction. Whether gender and/or age influence the relationship between infarct size, infarct severity, and left ventricular ejection fraction (LVEF) is unclear.Methods. We examined 460 patients (359 men) with acute myocardial infarction submitted to successful primary percutaneous coronary intervention. Infarct size, infarct severity, and LVEF were evaluated with perfusion gated SPECT at one month of index infarction.Results. There were no significant correlations between age and infarct size or infarct severity, and between age and LVEF. Moreover, elderly age ( ‡75 years) did not influence the relationship between LVEF and infarct size or infarct severity. Conversely, there was a significant gender-related difference in the relationship between LVEF and infarct size (F 5 20.5, P < .00001), and between LVEF and infarct severity (F 5 8.6, P < .005). In practice, there was a steeper decrease in LVEF in case of moderate to large infarct size in women than in men.Conclusion. With increasing infarct size, LVEF decreases more sharply in women than in men. Conversely, age does not influence the relationship between infarct dimensions and LVEF. (J Nucl Cardiol 2010)