The 3-4th intercostal space at the left border of the sternum is one of the important anatomical landmarks of the body. Many congenital heart diseases and heart valve diseases can be detected at the 3-4th intercostal space at the left border of the sternum by auscultation and other examinations, so the location of the 3-4th intercostal space at the left border of the sternum is very important. For children, infants, or adult males, the nipple is relatively constant, and the nipple is located at the position of the 4th intercostal space. This position is slightly inward to the side of the chest, which is the 4th intercostal space at the left border of the sternum, and then upward to the 3rd intercostal space at the left border of the sternum. For adult women, the position of the nipple varies with body position. This is where the 4th intercostal space should be located by the sternal angle. The first intercostal space is usually not felt from the body surface, and the intercostal space immediately below the left edge of the sternal angle is the second intercostal space at the left edge of the sternum, and immediately below that is the third intercostal space at the left edge of the sternum and the fourth intercostal space at the left edge of the sternum. Many common cardiac lesions such as congenital heart disease and aortic valve disease can be detected by auscultation of the 3rd-4th intercostal spaces at the left edge of the sternum.