The purpose of this study is to look at the effects of the drug Ranolazine compared to Placebo on symptoms of chest pain or chest tightness (known as angina), exercise endurance and ability, and changes in blood flow to the very small arteries of the heart (known as coronary microvascular function) in patients who do not have significant blockages in their major heart arteries. Ranolazine is a drug that is already approved by the FDA for angina, but it may be particularly effective in people with disease in their tiny heart vessels (known as coronary microvascular disease).