A novel monolithic multilayered ferrimagnetic-ferroelectric multiferroic heterostructure shows a remarkably large tuning of the magnetic response with an electric field. The heteroepitaxial stack is comprised of a near single crystal yttrium iron garnet (YIG) layer, a ferroelectric barium strontium titanate (BSTO) layer with good electric field tunability, and embedded platinum (Pt) electrodes.