Two prolate elements (region 1: lambda tricubic Hermite; mu,theta trilinear; pressure nodally interpolated) of pole zero material with is inflated to 1kPa. 2 ventricular cavity elements (region 2) are added and the reference state for the cavity elements is updated to be the deformed shape of the inner wall surface. Contractile forces are activated to simulate isovolumic contraction of the wall (ie cavity volume constant). As the contraction is applied the cavity pressure increases.