In this article we propose a cardiac motion estimation technique that uses non-rigid registration to compute the dense cardiac displacement field from 2D ultrasound sequences. Our method employs a semi-local deformation model which provides controlled smoothness. We apply a multiresolution optimization strategy for better speed and robustness. To further improve the accuracy, the sequence is registered in both forward and backward directions. We calculate additional parameters from the displacement field, such as total displacement and strain. We create an artificial ultrasound sequence of one heart cycle using a motion model and use it to validate the accuracy of the algorithm. Finally, we present results on real data from normal and pathological subjects that show the clinical applicability of our method.