In the past, it was believed that erectile dysfunction (ED) was mainly caused by psychological factors, but in fact, more and more information shows that more than 70% of ED is caused by organic factors, diabetes, cardiovascular disease, etc. can also lead to ED, even hypotensive drugs can cause erectile dysfunction. Recent studies have shown that a significant proportion of ED patients have vascular endothelial diastolic dysfunction. The endothelium is a single layer of flattened epithelium lining the luminal surface of the blood vessels, and in some older concepts the endothelium is just a mechanical barrier that provides a smooth physical surface for the flow of blood. With the rapid changes in science and technology, people’s views have also undergone profound changes. In recent years, some new views have suggested that the vascular endothelium is a very active endocrine organ with a variety of important biological activities, which can sense physiological stimuli and make regulatory responses to maintain the balance of the intravascular environment. Vascular endothelial cells play a very important role in the process of penile erection. Penile erection is a series of neurovascular activities, if the endothelial function of the blood vessels is impaired due to age, metabolic disorders, smoking, sedentary, obesity, etc., it will cause an imbalance in the substances that produce or act on the walls of the blood vessels to relax or contract the blood vessels, and thus impotence. The pathogenesis of many cardiovascular diseases is the same as ED, also from the decline in vascular endothelial function, causing functional and structural changes, and finally inducing various cardiovascular diseases. The introduction of the first phosphodiesterase type 5 (PDE5) inhibitor in 1998 brought a breakthrough in ED treatment, and the idea that ED can be effectively treated is now generally accepted. Although PDE5 inhibitors have been effective in treating ED, patient expectations are also rising. Patients expect more than just temporary help with erection, but expect to help restore erectile function. Rather than planning to have sex after taking the drug, patients expect to be able to have sex more naturally and spontaneously. As a result, long-term, low-dose daily PDE5 inhibitors have been proposed to help patients sustain improvements in erectile function and to enable them to have sex more naturally. A study of tadalafil (5 mg) in patients with ED treated for 12 weeks found that erectile function improved gradually over the course of the drug, with significant improvement in IIEF-5 scores after the fourth week of treatment and a significant increase in successful vaginal penetration and completion of intercourse. After discontinuation, a decrease in IIEF-5 scores was observed with prolonged discontinuation, but they were still well above the pre-treatment baseline levels. This suggests that the longer period (12 weeks) of daily PDE5 inhibitors restored erectile function, allowing the patients to continue to have sex naturally after discontinuation of the drug and to meet their treatment expectations. A few of these patients experienced side effects associated with PDE5 inhibitors, such as nasal congestion, headache, and back pain, but they were mild and well tolerated. The pharmacokinetic analysis of tadalafil shows that its half-life is 17.5 hours, and its blood concentration level can be maintained at a balanced level of 1.6 times the single dose for 5 consecutive days, so it is suitable for long-term low-dose treatment of ED.