We report on scanning tunneling microscopymeasurements of the piezoelectric response in ferroelectricheterostructuresgrown by off-axis rf magnetronsputtering. The samples are composed of a single-crystalline ferroelectricfilm of Pb(Zr0.2Ti0.8)O3deposited on a conducting substrate and covered with an ultrathin metallic film of gold. The high quality of the c-axis oriented ferroelectric layer is evidenced by sharp polarization hysteresis loops. By applying a voltage to the bilayer and recording the inverse piezoelectric effect with the scanning tunneling microscope, we demonstrate the ability to measure the phase response as well as the ferroelectric switching. We obtained strain-field plots with a butterfly loop shape, and a quantitative measurement of the longitudinal piezoelectric coefficient (d33).