['Impaired left ventricular (LV) diastolic function is a common pathophysiological feature of patients with hypertrophic cardiomyopathy (HCM). High-normal thyrotropin (thyroid-stimulating hormone, TSH) levels may alter the performance of the left ventricle.', 'To ascertain whether the severity of impaired LV diastolic function in HCM patients might worsen with elevating TSH levels within the reference range.', 'This study included 152 HCM patients and 119 healthy controls with euthyroidism. Blood samples were taken to test for serum TSH, free triiodothyronine (FT3) and free thyroxine (FT4) levels. LV diastolic function was quantified by determining the ratio of the transmitral early LV filling velocity to the early diastolic mitral annulus velocity (E/Ea ratio).', 'The E/Ea ratio was significantly higher in patients with high-normal TSH levels (25.7 ± 5.6 vs. 17.7 ± 4.9, p < 0.001). There was a significant correlation between the E/Ea ratio and the TSH levels within the high reference range (β = 0.268, p = 0.021). Univariate logistic regression showed that high-normal TSH levels were predictors of severe heart failure. However, after adjusting for the effect of LV diastolic dysfunction, high-normal TSH levels were no longer independent predictors of severe heart failure.'] Is a high-normal thyrotropin level associated with the severity of left ventricular diastolic dysfunction in patients with hypertrophic cardiomyopathy?