The devices and method described herein allow for therapeutic damage to increase volume in these hyperdynamic hearts to allow improved physiology and ventricular filling and to reduce diastolic filling pressure by making the ventricle less stiff. For example, improving a diastolic heart function in a heart by creating at least one incision in cardiac muscle forming an interior heart wall of the interior chamber where the at least one incision extends into one or more layers of the interior heart wall without puncturing through the interior heart wall and the incision is sufficient to reduce a stiffness of the interior chamber to increase volume of the chamber and reduce diastolic filing pressure.