A finite element (FE) analysis and an optimization algorithm were employed to assess the nonlinear passive elastic properties of left ventricular myocardium in a canine mode. The three-dimensional (3-D) left ventricular (LV) geometry was reconstructed at various times in the passive diastolic expansion phase using cross-sectional echocardiographic images. With the ventricular chamber pressure measured during the acquisition of the images as the load in the FE analysis, the computer predicted chamber expansion was compared with the actual expansion from the experimental data. An optimization algorithm was used to modify the assumed material property until the difference between the computer predicted and the actual expansion was minimized. By performing the analysis in a step-wise linear fashion for several time increments in diastole, the values of elastic modulus for the myocardium were determined as a function of left ventricular chamber pressure. The results from four experiments indicated a linear elastic modulus-chamber pressure relationship demonstrating that the left ventricular myocardium can be described using an exponential stress-strain relationship during the passive expansion phase. These results can potentially be used to assess the changes in the myocardial material properties in diseased states.