The benefit of stem and progenitor cell therapy for myocardial infarction (MI) is controversial. In this study the effect of MN-CBCs on survival and heart function after MI was analyzed. Methods: MI was induced in 14 weeks old male spontaneously hypertensive rats by ligation of left coronary artery (n=60) and 3x106 CFSE-labeled MN-CBCs (n=23) or medium (n=23) was injected via a tail vein. MN-CBC or medium injected sham-operated rats served as further controls (n=24). Eight weeks after MI right and left ventricular (RV and LV, respectively) function was measured with Millar-tip catheters and the hearts analyzed. Additional 12 infarct hearts were examined 6 or 24 h after cell or medium injection (each n=3). Results: Labeled cells were detected in the border zone adjacent to the infarct area at 6 and 24 h after cell injection (30 or 48 h post-MI, respectively). Cumulative survival, however, was comparable in cell and medium treated MI rats (57 vs. 61%, respectively) and MI size not significantly different (51±2 vs. 53±2%). Moreover, LV end-diastolic pressure (26±1 vs. 25±2 mmHg) and RV systolic pressure (55±5 vs. 58±6 mmHg) indicating severely impaired heart function were similar. Also the other hemodynamic parameters as well as the histological analyses did not provide evidence for improved myocardial pump function or cardiac remodeling after MI by MN-CBC therapy.