Objective: To establish a yielding criterion for porcine thoracic aorta. Methods: The thoracic aortas of three healthy pigs were used in order to form three testing groups: Group D, included aortic Dactyl tissues (n=8); Group C, included aortic Circumferential tissues (n=8); and Group L included aortic Longitudinal tissues (n=8). These groups were tested in a uniaxial tension device in order to determine the mechanical properties of the vessel. Results: Stress-Strain analysis of testing groups showed that for Low strain level (e=0.5) Stress of D group (S-D) was statistically (S, p < 0.01) greater than that of C and L groups (S-D > S-C and S-D > S-L, S); for medium strain level (e=1, S-D > S-L, S); for high strain level (e=1.5, S-D > S-C, S-D > S-L, S-C > S-L,S); and for yielding strain level e=2.1 (S-D > S-C, S-D > S-L, S-C > S-L,S). Additionally, mathematical elaboration of yielding data produced a criterion defined as: S-C∧2+S-L∧2=(S-C+S-L)/3*S-D. Conclusions: Although the derived yielding criterion refers to healthy porcine thoracic aorta, however, it predicts that tensile stresses, compressive stresses or a combination of them may simultaneously be present in physiological and pathological situations (i.e. atherosclerosis). Thus, it should be taken into account that patients with seemingly, trivial atherosclerotic stenoses deserve early treatment because certain minor events (i.e. blood pressure fluctuations) may trigger a fatal stress combination that could make aortic wall yield. Since the increased Cu concentration in aortic tissue results in diminished elastic properties of the vessel, it is obvious that, the present outcome along with recent evidence-regarding the effect of high Cu level in atherosclerosis (US2003000388213)-may also contribute to a deeper understanding of plaque rupture behavior.