Cardiac ultrasound AO is the abbreviation for the internal diameter of the aorta in cardiac ultrasound. The aorta is the arterial backbone of the circulation, emanating from the left ventricle, with its branches supplying the whole body with blood circulation, and the inner diameter of the aorta has a normal value of 20~35mm. if the cardiac ultrasound examination suggests that the AO increases, it suggests that there is a high probability of aortic regurgitation, and if it suggests that the AO decreases, it suggests that there is a high probability of aortic stenosis. Cardiac ultrasound is an inexpensive and non-invasive examination that can dynamically display the structure of the heart chambers, the beating of the heart and the direction of blood flow, as well as whether the thickness of the heart septum is normal or not, and whether the ejection fraction is normal or not. Cardiac ultrasound is an effective means of examining the structure and function of the heart chambers and the surrounding large blood vessels.