And if shows up a a nuclear pet scan and there is no blockage after a cardio cat. what could be done to prevent problems(heart attack, or worse?

Good diet & exercise: Your PET scan shows no trouble today (good!) but don't confuse medical tests with a crystal ball (as many folks do) - they're not able to predict the future. To assure continued good health, you must minimize your risk factors: no smoking, normal weight, daily exercise, no recreational drugs esp cocaine/amphetamines, minimal alcohol.