The invention relates to the treatment of diastolic dysfunction in a subject, and relates in particular to compositions for use and methods in treating diastolic dysfunction. In one aspect the invention provides a composition for use comprising a therapeutically effective amount of a substance which increases the level and/or activity of a crystalline protein in cardiomyocytes of the subject. In particular the composition for use according to the invention comprises a therapeutically effective amount of the alpha B crystalline protein. It was found that the composition for use is capable of treating diastolic dysfunction and diastolic heart disease in subjects with failing hearts that have a higher cardiomyocyte stiffness than controls. Particularly, addition of alpha B crystalline reduced the higher stiffness of failing cardiomyocytes to the level observed in control cardiomyocytes.
