The primary reason body builders and athletes want AICAR is because it greatly increases blood flow to the heart. It has been used for this by the medical community since the late 1980s. It also greatly increases the body's ability to use glucose - so you have both more blood flow through the heart AND more energy in your cells. If used 24 hours before heart surgery, it lengthens the time the heart cells can be without blood flow and not die.
As if that is not enough, it also has recently (last 4 or so years) been found to have anti-cancer properties. It helps prevent cancerous cells from dividing, thereby spreading throughout the body. It also helps prevent the corruption of healthy cells by the cancerous cells. Clinical human trials are still underway for at least 3 different types of cancer (colon and lymphoma are the only two I remember).