A warning sign for impending cardio-vascular events is not fully established. In the process to plaque rupture, formation of vulnerable plaque is important, and oxidized cholesterols play important role in its progression. Furthermore, the significance of vasa vasorum penetrating medial smooth muscle layer and rich in atheromatous lesion should be paid attention. Cardio-ankle vascular index (CAVI) is new arterial stiffness index of the arterial tree from the origin of the aorta to the ankle. CAVI reflects functional stiffness in addition to structural stiffness. Rapid rise of CAVI means medial smooth muscle cell contraction, and strangling vasa vasorum. We reported rapid rise of CAVI in peoples after big earthquake, following high frequency of cardiovascular events. And we met several cases who showed rapid rise of CAVI a few weeks or months before suffering cardiovascular events. To explain these sequences of events, we proposed a hypothesis; A rapid rise of CAVI means medial smooth muscle contraction, strangling vasa vasorum, leading ischemia, necrosis of vulnerable plaque, then, the plaque ruptures. In individuals having high CAVI, further rapid rise of CAVI might be a warning sign for impending cardiovascular events. In such case, treatments to decrease CAVI had better to be taken soon.