Now that you have reviewed normal blood flow, why does a patient with left-sided heart failure have a low systolic blood pressure? choose the best answer. choose the best answer. the left side of the heart contains the ventricles, so it controls blood pressure. the left side of the heart does not directly move blood into the body, but when it fails, the right side will also fail, and that will decrease blood pressure out in the body. the left side of the heart pumps blood into the body, so when it fails, less blood will be pumped into the arteries. the left side of the heart receives blood from the body, so when it fails, blood will build up in the blood vessels.