The circulatory system is important because it transports o2 in blood. O2 is important because all living thing need it. Involuntary muscles are muscles you can’t control. First the blood containing co2 enters the heart through the right atrium. Next the left ventricle contracts with involuntary muscles the blood to the lungs to exchange co2 with o2. Next the blood containing o2 is pumped to the hearts left atrium. The atrium contracts pushing the blood to the left ventricle. Then the ventricle contracts pushing the blood into your arteries. Your blood is pushed through arteries to deferent locations. Next the blood does a second o2 and co2 exchange. Your blood exchanges o2 with co2. Next the blood containing co2 is pumped to the heart’s right atrium where the process repeats.