Most cases of lower blood pressure are related to cardiovascular causes. The causes are: first, insufficient blood volume, which can be seen in patients with massive blood loss from trauma, and patients who drink less water in a hot environment leading to dehydration. Second, drug overdose, hypertensive patients who take too much antihypertensive drugs for various reasons can also experience a decrease in blood pressure. Third, serious heart disease, various causes of heart failure, to the end stage can be manifested as stubborn hypotension, not easy to correct. If a patient with normal blood pressure suddenly develops lower blood pressure for no apparent reason, the common diseases are acute myocardial infarction and fulminant myocarditis, and early improvement of cardiac ultrasound examination can help to make a clear diagnosis. Fourth, individual variability, seen in patients with a thin and weaker physique, slightly lower than normal blood pressure, if there are no uncomfortable symptoms, no special treatment is required.