Biaxial mechanical behavior of excised ventricular epicardium

We present results from in vitro biaxial stress-strain experiments on epicardium excised from the right and left ventricular free walls of canine hearts. These data reveal that the biomechanical behavior of ventricular epicardium is qualitatively similar to atrial epicardium and parietal pericardium but different from noncontracting myocardium. In particular, ventricular epicardium exhibits a highly nonlinear stress-stretch behavior, being initially compliant but then very stiff near the limits of its extensibility. In addition, the epicardium appears to be initially isotropic but becomes markedly anisotropic upon rapid stiffening. Finally, specimens taken from the right and left ventricular free walls behaved similarly. We submit that excised ventricular epicardium is capable of carrying significant in-plane loads and that there is a need to investigate further its role in local and global cardiac mechanics and physiology.