deoxidized blood comes from the body, which then goes into the superior/inferior vena cava and makes its way to the right atrium, the right atrium contacts and forces blood through the tricuspid valve and the pulmonary semilunar valve into the pulmonary trunk/arteries, the pulmonary arteries carries blood tot he lungs and it then enters the alveolar capillaries where the gas exchange happens and drops off carbon dioxide and picks up oxygen, oxygenated blood flows into the left atrium from the pulmonary veins, blood gets pumped in to the mitral (bicuspid) valve into the left ventricle, the left ventricle contracts and the the aortic semilunar valve opens and pumps blood into the aorta for distribution to the systemic circuit of the body