Extracellular volume (ECV) has been validated as a surrogate measure of interstitial fibrosis, that is increased in both hypertension-induced left ventricular hypertrophy (H-LVH) and hypertrophic cardiomyopathy (HCM). We aimed to explore the correlation between ECV and left ventricular cardiac function. Eighty-one patients with HCM, 44 with H-LVH and 35 controls were prospectively enrolled. Even among patients with normal diastolic function, patients in HCM group had increased- ECV. In terms of diastolic dysfunction (DD), a similar increase in ECV was associated with a larger percentage of patients with severe or moderate-to-severe DD in HCM group. In addition, there was a compensatory increase in the left ventricular ejection fraction (LVEF) in HCM, but no hyperdynamic LVEF was observed in H-LVH. ECV was negatively correlated with LVEF in the late gadolinium enhancement (+) (LGE+) subgroups in the H-LVH group, while no significant linear correlation was observed in HCM group. The increased ECV in HCM patients with normal diastolic function warrants further exploration of the prognostic value of ECV assessments in the early stages of HCM. The associations between ECV and left ventricular functional parameters differed and taking both LGE and ECV into account might be reasonable way to differentiate between the two disorders.