There are 4 study visits (2 visits in each study period) in this study. Subjects will be in this study for about 6 weeks from Week 0 - baseline visit to Week 6 - exit visit. Besides the procedure of study medication mentioned above, other study procedures include informed consent, physical exam, questionnaires, EKG for safety assessment, blood collection for laboratory testing, cardiac MRI, and follow-up events. In sum, participants will be asked to undergo 2 cardiac MRI's and fill out questionnaires 4 times. They will be asked to participate for 6 weeks with two 2-week courses (with a treatment window period of 5 days), one with ranolazine and the other with placebo (without knowing which they are taking). There is a 2-week washout period between treatments. The participants will otherwise remain on all their usual medications. The physicians will also be blinded to which medication the subject is receiving.