小儿循环系统因年龄不同具有以下解剖生理特点:①心脏体积和重量相对地比成人大。如新生儿心脏重量约为20～25克,是体重的0.7％。而成人心脏重约2500～3500克,占体重的0.5％。②小儿心脏的位置随年龄而异。2岁以下的小儿心脏多呈横位,以后随年龄增加,由于直立行走,胸部及肺的发育和膈肌下降,心脏渐渐变为斜位。因此,新生儿心尖搏动位置在左侧第3～4肋骨乳头线外。6～7岁时心尖搏动在左肋第5肋间乳头线上。12岁后在乳头线内 Pediatric circulatory system due to different age has the following anatomical and physiological characteristics: ① heart size and weight are relatively larger than adults. If the newborn heart weight is about 20 ~ 25 grams, 0.7% of body weight. The adult heart weighs about 2500 ~ 3500 grams, accounting for 0.5% of body weight. ② children’s heart position varies with age. The heart of children under 2 years of age was mostly horizontal, and later with age, due to upright walking, chest and lung development and diaphragmatic decline, the heart gradually became oblique. Therefore, the newborn apical beating position in the left 3 to 4 ribs outside the nipple line. 6 to 7 years old apical beating in the left rib 5 intercostal nipple line. 12 years old in the nipple line