The duration of the effect of phentolamine is related to the route of administration and the patient’s physical condition, for example, it takes effect immediately after intravenous injection, and the effect disappears within minutes after the drug stops being administered intravenously. Phentolamine is a short-acting non-selective alpha1 and alpha2 receptor blocker, which, through the blocking effect of alpha receptors and vasodilating effect, causes a decrease in peripheral resistance of the heart, a decrease in blood pressure, and also causes tachycardia. It can be used in the treatment of heart failure, pheochromocytoma and other diseases. The duration of action depends on the mode of administration and the patient’s physical condition. Phentolamine is usually administered orally and its duration of action in the body lasts 3-6 hours, while when administered intravenously, the effect is immediate. In addition, because the common adverse effects of phentolamine are postural hypotension and arrhythmia, blood pressure and heart rhythm should be checked during administration; also use with caution in patients with myocardial infarction and hypotension.