The school nurse was asked to teach a class on the circulatory system to a group of high school students. Place in the correct order the flow of blood through the heart as the nurse presents it, starting with the entry of blood to the heart and ending with the exit of blood into the arterial circulation.

The correct sequence for blood flow through the heart begins with deoxygenated blood entering the right atrium via the inferior and superior vena cava (index 3). From there, blood passes through the tricuspid valve into the right ventricle (index 5). The right ventricle then pumps blood through the pulmonary valve and into the pulmonary artery to reach the lungs (index 0). In the lungs, gas exchange occurs and deoxygenated blood becomes oxygenated (index 4). Oxygenated blood returns from the lungs to the left atrium and passes through the mitral valve into the left ventricle (index 1). Finally, the left ventricle contracts and ejects blood into the aorta, distributing it to the rest of the body (index 2). This sequence — 3, 5, 0, 4, 1, 2 — represents the complete path of pulmonary and systemic circulation through the heart. A common error students make is confusing the tricuspid and mitral valves or misplacing oxygenation before the pulmonary artery. The tricuspid valve separates the right atrium and ventricle; the mitral valve separates the left atrium and ventricle. Oxygenation occurs in the pulmonary capillaries after the blood travels through the pulmonary artery, not before. Understanding this ordered pathway is foundational to interpreting cardiac and respiratory pathophysiology.