The midclavicular line is the plumb line from the sternal end of the clavicle to the midpoint of the acromion end of the clavicle. The midclavicular line has great significance in clinical practice. 1. It can be used as a fixed point for thoracic puncture. From the sternal end of the clavicle to the acromion end of the clavicle, the midpoint of the distance between the two is used as a marker, and a plumb line parallel to the midline is made downward from this marker, which is called the midclavicular line. In the case of pneumothorax, thoracentesis is usually performed at the second intercostal space of the midclavicular line. 2. In adult men and children, the midclavicular line passes 0.5 to 1 centimeter medial to the nipple. The midclavicular line is used to determine the location of the apex of the heart, which is located at the junction of the fifth intercostal space and the midclavicular line. The midclavicular line is an important surface landmark of the body and better helps in localization. If there is any discomfort, please consult your physician at the hospital.