Select the correct statement about the three-chambered hearts of amphibians and nonbird reptiles. A scheme of blood circulation of reptiles except for birds. The reptiles have a three-chambered heart that consists of two atria and one ventricle with an incomplete septum. There are two circuits: pulmonary and systemic. In the pulmonary circuit, the blood from the right ventricle is pumped in to lung capillaries and returned to the left atria. In the systemic circuit, the blood is pumped from the left ventricle to the systemic capillaries via the left systemic aorta and is then returned to the right atria. There is also one vessel going from the right ventricle to the aorta right before it branches to smaller arteries. This vessel carries mixed blood. All blood on the right side of the circuits is venous and all blood on the left side is arterial. Select the correct statement about the three-chambered hearts of amphibians and nonbird reptiles. The three-chambered hearts of amphibians and nonbird reptiles are facultative, allowing variation in blood flow through the heart. The three-chambered heart is inferior to the four-chambered hearts of birds and mammals, limiting the evolutionary success of amphibians and nonbird reptiles. Pulmonary and systemic blood fully mixes in the ventricle of a three-chambered heart.