Cohort A: Overt & Diagnosed PA  Inclusion Criteria:  Adults aged 18-85 Able to provide informed consent and willing to comply with the study Able to fit safely in PET/CT scanner (weight limit 500 pounds; diameter and circumference of PET/CT scanner are 70 cm and 220 cm, respectively) Hypertension treated with at least one antihypertensive drug Cohort A: Clinically confirmed diagnosis of PA not yet treated with mineralocorticoid receptor antagonists  Exclusion Criteria:  History of MI, CABG, known cardiomyopathy (EF <40%, hypertrophic cardiomyopathy, and/or amyloid), cardiac transplantation Contraindication or allergy to eplerenone or spironolactone Current pregnancy or breastfeeding eGFR < 45 mL/min/1.73m2 or potassium > 5.1 on labs within the preceding 3 months Cohort A: Planned adrenalectomy in the subsequent 6 months  Cohort B: Subclinical & Undiagnosed PA  Inclusion Criteria:  Adults aged 18-85 Able to provide informed consent and willing to comply with the study Able to fit safely in PET/CT scanner (weight limit 500 pounds; diameter and circumference of PET/CT scanner are 70 cm and 220 cm, respectively) Hypertension treated with at least one antihypertensive drug Cohort B: Clinically indicated cardiac PET perfusion scan within the preceding 3 months and echocardiogram within the preceding 6 months  Exclusion Criteria:  History of MI, CABG, known cardiomyopathy (EF <40%, hypertrophic cardiomyopathy, and/or amyloid), cardiac transplantation Contraindication or allergy to eplerenone or spironolactone Current pregnancy or breastfeeding eGFR < 45 mL/min/1.73m2 or potassium > 5.1 on labs within the preceding 3 months Cohort B: 10% or greater burden of ischemia on qualifying PET Cohort B: Planned coronary angiogram/revascularization in the subsequent 6 months.