RecruitingClinical trialUPBEAT: Using Polygenic Scores to Guide BB Therapy in HF With Mildly Reduced EFThis study will use polygenic scores, a tool which describes differences in genetics, to examine effectiveness of beta blocker medication in heart failure patients with ejection fraction of 41-50 percent. The study will also assess beta blockers' effect on the changes in left ventricular end-systolic volume index by MRI.