The reprogramming of adult cells into pluripotent cells or directly into alternative adult cell types holds great promise for regenerative medicine. We reported previously that structural cells in the heart called cardiac fibroblasts, which represent 50% of the cells in the mammalian heart, can be directly reprogrammed to beating heart muscle-like cells in petri dishes. This work builds on our previous findings by using mice that had experienced a heart attack. We delivered three genes that normally guide embryonic development (abbreviated as GMT) directly into the damaged region of the mouse heart. Within a month, non-beating cells that normally form scar tissue transformed into beating heart cells. Within three months, the hearts were beating even stronger and pumping more blood. When this experiment was performed with GMT and the additional delivery of a protein called thymosin beta 4, which encourages blood vessel growth, the improvements in scar area and cardiac function were even more pronounced. These findings demonstrate that cardiac scar tissue can be transformed into heat muscle-like cells in their native environment for potential regenerative purposes.