The infant's circulatory system, arteriovenous cardio-vascular system, pediatrics. This medical illustration shows the cardiovascular system of a young boy aged 1 to 2. At this age, the heart is still in a horizontal position. Its full development will occur around the age of 5. Therefore, the infant's heart muscle is immature and vulnerable to heart failure. In this illustration, the arteriovenous circulation is detailed at the level of the various organs, including the lungs, liver, kidney and digestive organs. But it is also detailed at the level of the head, and the upper and lower limbs. Finally, the heart is shown in section, highlighting the parts of the venous and arterial circulation.