The investigators present a rare case of myofibrillar cardiomyopathy in an 18-year-old male patient in which echocardiography, cardiac magnetic resonance, and genetic testing played complementary roles. At the top, the parasternal long- and short-axis views of the heart document increased wall thickness and normal systolic function. Significant diastolic dysfunction was present. Cardiac magnetic resonance imaging (bottom) showed delayed enhancement in thickened segments and was not suggestive of cardiac amyloid or hypertrophic cardiomyopathy. Quadriceps muscle biopsy showed histopathology compatible with myofibrillar myopathy. Subsequent genetic testing confirmed a novel desmin gene mutation as the cause.