A method and a device for improving cardiac function are provided. The device is packaged in a collapsed state in an end of a catheter. Portions of a frame construction of the device spring outwardly when the catheter is withdrawn from the device. Anchoring formations on the frame construction secure the frame construction to a myocardium of the heart. A membrane secured to the frame construction then forms a division between volumes of an endocardial cavity of the heart on opposing sides of the membrane.