A heart rate of 120 suggests that there is some possibility of respiratory failure, but a fast heart rate is not a diagnostic criterion for respiratory failure. The diagnosis of respiratory failure mainly relies on arterial blood gas analysis. 1. When the partial pressure of oxygen in arterial blood is <60mmHg and the partial pressure of carbon dioxide is normal or decreasing, the diagnosis is type I respiratory failure. 2. When the partial pressure of oxygen in arterial blood is <60mmHg and the partial pressure of carbon dioxide is >60mmHg, the diagnosis is type II expiratory failure. A heart rate of 120 suggests that the heart rate is too fast, and when the patient has a prolonged fast heart rate, it is often complicated by pulmonary edema. Pulmonary edema is caused by the increase of lung water, resulting in interstitial thickening, leading to oxygen diffusion dysfunction, causing a decrease in arterial partial pressure of oxygen, resulting in respiratory failure. It is recommended to consult a doctor in time to avoid delaying the condition.