The purpose of this study is to determine whether taking losartan helps people with hypertrophic nonobstructive cardiomyopathy feel better by decreasing the amount of heart muscle thickening and/or the amount of heart muscle scarring.

Hypertrophic cardiomyopathy (HCM) is characterized by idiopathic cardiac hypertrophy, heart failure, ischemia even in the absence of epicardial coronary artery disease, and arrhythmias. The pathological features of HCM include hypertrophy and disarray, interstitial fibrosis, and increased arteriolar wall thickness. Hypertrophy and fibrosis are major determinants of morbidity and mortality in hypertrophic cardiomyopathy. Some investigators have demonstrated that interstitial fibrosis and hypertrophy occur secondarily, in response to trophic and mitotic factors in the heart. Therefore, blocking trophic factors may attenuate or potentially reverse hypertrophy and fibrosis in HCM.

Angiotensin II has trophic and profibrotic effects on the heart, and blockade of angiotensin II type I receptors has been shown to attenuate myocardial hypertrophy and fibrosis in acquired cardiac disease in humans and animal models.

We hypothesize that treatment with the selective angiotensin II type receptor antagonist, losartan, will decrease both hypertrophy and fibrosis, improve diastolic function, reduce symptoms, and improve functional status in patients with HCM.

Inclusion Criteria:

• Patients with hypertrophic cardiomyopathy
• Left ventricular outflow tract (LVOT) gradient less than 30 mm Hg at rest
• Age 18 years or older

Exclusion Criteria:

• Contraindication to losartan
• Already taking losartan
• Contraindication to MRI
• Hemodynamic instability