A new modeling approach using two different zero-load geometries (diastole and systole) was introduced to properly model active contraction and relaxation for more accurate stress/strain calculations. Ventricle diastole and systole material parameter values were also determined based on in vivo data. Echo image data were acquired from 10 healthy volunteers at the First Affiliated Hospital of Nanjing Medical University with consent obtained. Echo-based computational two-layer left ventricle (LV) models using one zero-load geometry (1G) and two zero-load geometries (2G) were constructed. Material parameter values in Mooney-Rivlin models were also adjusted during the cardiac cycle to match Echo volume data. Effective Young’s moduli (YM) were calculated for ventricle materials for easy comparison.

Using the mean values of the 1G models as the baseline values, at begin-filling, the mean YM value for the fiber direction (YM_f) from the 2G model was 107% higher than that from the 1G model (723.57 kPa vs. 348.71 kPa). At begin-ejection, YM_f from 2G model was 47% lower than that from the 1G model (85.48 kPa vs. 162.77kPa). According to the total average values, begin-ejection stress and strain from the 2G model were 30% and 14.5% higher than that from the 1G model, respectively (345.16 kPa vs. 265.62 kPa; and 1.0489 vs. 0.9161). Begin-filling stress and strain from the 2G model were 11.5% and 55% higher than that from the 1G model, respectively (2.2613 kPa vs. 2.5543 kPa; and 0.0489 vs.0.1085). During a cardiac cycle, the 2G model begin-ejection YM_f, stress and strain were 19%, 495% and 29% higher than their end-filling value, end-ejection YM_f, stress and stain were 49%, 605% and 297% higher than their begin-filling value, respectively.

The 2G model took ventricle zero-load geometry difference between systole and diastole phases into consideration. This may lead to more accurate ventricle stress/strain calculations and material parameter value estimations.