Different shear wave elastography methods have been proposed to measure cardiac material properties. This study compared shear waves naturally generated by aortic and mitral valve closure to those externally induced with an acoustic radiation force throughout the cardiac cycle. The shear wave timing and propagation speeds were measured in four pigs with open-chest recordings. Despite spatial and temporal differences in excitation source, the propagation speeds of the natural shear waves were found to be in the same range as the propagation speeds of the active shear waves. The results also suggested a large inter-beat variability for the natural shear waves.