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 mice that have 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. This process is more difficult to achieve in a petri dish, but would be useful for testing new drugs for personalized medicine or modeling cardiac disease in a dish. Here, we describe a detailed, step-by-step protocol for reprogramming cardiac fibroblasts in a dish using a retrovirus to introduce the GMT genes into the cells. Developing standardized protocols will help research laboratories master the procedure and develop the technology further. Initial evidence of reprogramming can be observed as early as three days after the procedures begin. The reprogrammed cells begin to beat in the dish after approximately 2 months.