Adipose tissue consists of mature adipocytes and a mononuclear cell fraction termed adipose tissue-derived cells (ADCs). Within these heterogeneous ADCs exists a mesenchymal stem cell-like cell population, termed adipose tissue-derived stem cells. An important clinical advantage of adipose tissue-derived stem cells over other mesenchymal stem cell populations is the fact that they can be isolated in real time in sufficient quantity, such that ex vivo expansion is not necessary to obtain clinically relevant numbers for various therapeutic applications. The aim of this investigation was to evaluate the therapeutic potential of freshly isolated ADCs in treating rats acutely following myocardial infarction. Rats underwent 45 min of left anterior descending artery occlusion followed by reperfusion. Fifteen minutes post-myocardial infarction, saline or 5 x 10(6) ADCs from green fluorescent protein-expressing transgenic rats were injected into the chamber of the left ventricle. Left ventricular function and morphometry was followed with 2-D echocardiography for 12 wk, at which point hearts were harvested for histological analysis. Twelve weeks following cell therapy, left ventricular end-diastolic dimension was less dilated while the ejection fraction and cardiac output of ADC-treated rats were significantly improved compared to control rats (P < 0.01). Despite this benefit, absolute engraftment rates were low. This paradox may be partially explained by ADC-induced increases in both capillary and arteriole densities. These data confirm the therapeutic benefit of freshly isolated ADCs delivered post-MI and suggest a novel beneficial mechanism for ADCs through a potent proangiogenic effect.