A and B, Functional improvement after myocardial infarction in transplanted rat hearts. Left ventricular ejection fraction (EF) and fractional shortening were analyzed by echocardiography for all 3 experimental groups in triplicate recordings: hCDCs (n = 6), cardiac fibroblasts (n = 4), and control (n = 5). A, At 7 days, *P = 0.08 and **P = 0.001 relative to the hCDC group; at 28 days, *P = 0.01 and **P = 0.004 relative to the hCDC group. B, *P < 0.05 relative to the hCDC group at 28 days.