Which chamber of the heart do you think is the most muscular? explain your reasoning. a growing fetus has a vessel, the ductus arteriosus, in the heart that connects the pulmonary artery with the aorta and conducts blood directly from the right ventricle to the aorta. why do you think this vessel closes soon after birth? in most of the body, the arteries carry oxygenated blood and the veins carry deoxygenated blood. the exception to this pattern is the heart. explain how and why specific arteries and veins of the heart are different from the pattern seen in the rest of the body. describe the mechanisms in place to prevent the blood from flowing in the wrong direction through the heart. explain what happens to tissues, such as the heart, or the brain, if oxygenated blood is not delivered in a timely manner?