Abstract Body (Do not enter title and authors here): Goals: Mavacamten not only promotes favorable cardiac remodeling in obstructive hypertrophic cardiomyopathy but can also unmask additional underlying structural abnormalities.

Description of Case:
An 80-year-old man with atrial fibrillation and basal septal hypertrophy with an intracardiac defibrillator, presented due to six months of exertional dyspnea.

Transthoracic echocardiography (TTE) revealed severe basal septal hypertrophy (1.7cm) and systolic anterior motion (SAM) of the anterior mitral valve leaflet (peak LVOT gradient 104 mm Hg; Figure 1). The patient was treated with metoprolol but presented again one month later with recurrent postural syncope. The metoprolol dosage was increased, and the patient was initiated on mavacamten.

12 weeks after initiation of mavacamten, surveillance TTE demonstrated a LVOT gradient of 7 mmHg at rest and 11 mmHg during Valsalva maneuver, and a basal septal wall thickness of 1.0 cm. Severe mitral regurgitation was noted with the mechanism identified as both Carpentier type I and II. The primary etiology of the regurgitation was determined to be P3 prolapse (Figure 2). There was no longer evidence of SAM.

The patient remained symptomatic and was referred to cardiothoracic surgery for mitral transcatheter edge-to-edge repair (mTEER). Post procedure, the patient’s dyspnea resolved. TTE showed the implanted Mitraclip with trace intra-valvular mitral regurgitation (Figure 3).

Discussion:
This patient likely had a multifactorial cause of dyspnea. Mavacamten improved the patient’s basal septal hypertrophy and SAM. Subsequent TTE revealed a previously undetected mitral regurgitation jet which was only apparent after the use of mavacamten. This finding led to resolution of symptoms with mTEER.