This trial aims to enroll 50 patients with angina who undergo baseline bicycle exercise testing with monitoring of the heart's electrical activity and oxygen consumption (known as cardiopulmonary exercise test) and coronary angiogram (taking pictures of the heart arteries through small hollow tubes placed through the wrist or groin). If severe blockages in the main arteries are not found then testing for coronary microvascular function will be performed. Subsequently, participants will then be randomized 50/50 to either Ranolazine or Placebo. After taking the study drug for 12 weeks, they will then repeat the cardiopulmonary exercise test and the coronary angiogram with testing for microvascular function.