The heart is beneath the breastbone in the chest cavity of the frog. It's simple sac-like lungs are located in the back , on either side of the heart. In frogs, which can also do cutaneous respiration(skin-breathers), the lungs are another place for oxygen and carbon dioxide to be exchanged, just like their thin moist skin is. Their three-chambered heart contains two atria and one ventricle. There is no separation of oxygenated and deoxygenated blood, therefore, there is mixing between the two. The ventricle pumps and some blood goes to the arteries to be transported to the cells of the frog's body, and some is transported to the lungs for gas exchange. The proximity of the heart and the lungs means it is a short distance for the blood to travel to the lungs, to absorb more oxygen. However, oxygen also enters the thin moist skin of the frog and goes into its capillaries for transport.