A 3D, nonlinear finite element (FE) model of the diastolic canine heart was constructed from multislice magnetic resonance images (MRI). The model was solved using the p-version of the FE method to predict stress and deformation in diastole. Finite element models were employed in an 'inverse' problem to estimate the nonlinear material properties of intact diastolic myocardium. Additionally, FE models were employed to examine the effects of RV pressure overload on LV pressure-volume (P- V) relationships in the pathologic heart. A 3D, nonlinear FE model had 1,704 degrees of freedom and 8 elements, it had a maximum principal stress value of 429,127 dynes/cm2 and a minimum principal stress of -344,599 dynes/cm2 at p equals 6. Average nonlinear material parameters estimated for 6 dogs were E equals 28,722 +/- 15,984 dynes/cm2 and c equals 0.00182 +/- 0.00232 cm2/dyne. Examination of the effects of RV pressure increase on LV P-V relationships indicated substantially different effects of RV pressure overload on the different pathologic conditions (p < 0.005 by ANOVA) with increasing RV pressure having a more pronounced effect on the dilated heart than the hypertrophied heart. When the mechanical effects of the pericardium were included in the model, at higher RV pressures, all of the pressure-volume (P-V) curves became similar indicating that at higher RV pressures, the P-V curves were independent of ventricular shape and material properties and depended only on the RV pressure. In conclusion, FE models of the heart were constructed from MRI images of the heart and were employed to study diastolic ventricular function in the normal and pathologic heart.