In this paper, Myocardial Elastography (ME), a radio-frequency (RF) based speckle tracking technique, was employed in order to assess the contractility of a myocardium, and validated against tagged Magnetic Resonance Imaging (tMRI) in vivo in normal as well as abnormal cases. Both RF ultrasound and tMRI frames were acquired in 2D short-axis (SA) views from two healthy subjects and one with a history of infarction. In-plane (lateral and axial) incremental displacements were iteratively estimated using ID cross-correlation and recorrelation techniques in a 2D search with a 1D matching kernel. The incremental displacements from end-diastole (ED) to end-systole (ES) were then accumulated to obtain cumulative systolic displacements. In tMRI, cardiac motion was obtained by a template-matching algorithm on a 2D grid-shaped mesh. The entire displacement distribution within the myocardium was obtained by a cubic B-spline-based method. In both ME and tMRI, 2D Lagrangian finite systolic strains were calculated from cumulative 2D displacements. Radial and circumferential strains were then computed from the 2D finite strains. Both qualitatively and quantitatively, ME is shown capable of measuring myocardial deformation in excellent agreement with tMRI estimates in normal and abnormal subjects.