Experimental studies have suggested that a bone marrow stem cell transplant into the heart produces a favorable impact on tissue perfusion, yielding a new perspective on myocardial regeneration. Studies in human beings have demonstrated an improved clinical and functional cardiac state, which has been explained mainly by the angiogenic potential of the stem cells. Our objective was to compare the functional outcome of mononuclear stem (MoSC) and mesenchymal stem (MeSC) cell therapy after myocardium infarction in rats. Forty-two rats with myocardial infarctions underwent autologous transplantation of MoSC and MeSC in animals with ejection fractions lower than 40%. The functional analysis was performed using echocardiography at baseline and at 1 month after direct injection into the ventricular wall using: 5 x 10(6) MoSC (n = 08) or 2.5 x 10(6) MeSC (n = 13) or medium controls (n = 21). Statistical significance was accepted when P < .05. Intragroup comparisons of baseline versus 1-month follow-up were performed with paired t tests. Kruskal-Wallis was used as appropriate. There was a difference in baseline left ventricular ejection fraction (LVEF) and left ventricular-end dyastolic volume between all groups. After 1 month, LVEF decreased in the control group but remained unchanged in MoSC and MeSC groups. In all groups we observed myocardial remodeling. In conclusion, we have not demonstrated functional effectiveness with either MoSC or MeSC cell type, but potentially improved myocardial perfusion needs to be analyzed.