The goal of this observational study is to measure the effect of mavacamten treatment on blood flow in the heart muscle (myocardium) in patients with obstructive hypertrophic cardiomyopathy. The main question it aims to answer is:

• Does mavacamten treatment improve blood flow in the heart muscle?

Participants will take mavacamten at the direction of their treating physician. Participants will complete 2 myocardial Positron Emission Tomography and Computed Tomography (PET-CT) scans. The first scan will be completed before participants start taking mavacamten. The scan will be repeated after 12 months of mavacamten treatment.

This is a single-arm, before-and-after investigation of the effect of mavacamten therapy on myocardial blood flows in adult human subjects prescribed mavacamten for clinical standard of care for oHCM. We hypothesize that 12 months of mavacamten therapy will improve myocardial blood flows as assessed by PET/CT. The investigation will take place at a single site. Participants who consent will be prospectively enrolled once mavacamten therapy has been approved by their health insurance/payer. Enrolled participants will undergo myocardial PET/CT before starting mavacamten and after 12 months of therapy.

Inclusion Criteria:

1. Willingness and ability to provide written informed consent
2. Willingness and ability to comply with scheduled visits and study procedures
3. Male or female, aged 18-85 years
4. Diagnosed with obstructive hypertrophic cardiomyopathy according to presence of a left ventricular wall thickness of ≥15 mm that is otherwise unexplained by abnormal loading conditions (e.g., hypertension, valvular, congenital disease) or infiltrative cardiomyopathies. Unexplained left ventricular wall thickness of ≥13 mm is sufficient for diagnosis in relatives of individuals with hypertrophic cardiomyopathy or those who are genotype positive.
5. Has been prescribed mavacamten consistent with US Prescribing Information
6. Ability and intention to adhere to oral mavacamten therapy as prescribed by treating physician for the duration of study participation
7. For females of reproductive potential: negative pregnancy test at screening/baseline and 12 month visits.

Exclusion Criteria:

1. Pregnancy or lactation
2. Known hypersensitivity to components of mavacamten or regadenoson
3. Prior treatment with mavacamten or aficamten

11. Over weight limit for imaging gantry. 12. To minimize the risk of participants undergoing PET/CT with inadequate image quality, participants with left ventricular systolic dysfunction or lung disease will be excluded.

Clinically stable adult obstructive hypertrophic cardiomyopathy patients on background therapy who have been prescribed Camzyos (mavacamten) in accordance with the US Prescribing Information, but who have not yet started this medication.

No data on individual participants will be shared outside the University of Virginia.