Heart failure, myocarditis, tachycardia, anemia, etc. can lead to fast and weak pulse. 1. Heart failure: When the blood pumped out by the heart is unable to meet the needs of the body, it can cause heart failure, which can lead to the symptoms of fast and weak pulse, as well as fatigue, shortness of breath during activities, palpitations and other symptoms. 2. Myocarditis: patients with myocarditis may have no obvious symptoms in the early stage, but in severe cases, they may have arrhythmia, dilated cardiomyopathy changes, and signs of fast and weak pulse. 3. Tachycardia: If the heart beats too fast, the heart may not be able to supply blood effectively, which may lead to hypoxia in some organs and tissues, and symptoms such as fast and weak pulse, panic, shortness of breath and chest tightness may appear. 4. Anemia: Anemia will lead to a significant reduction in the effective circulating blood volume in the body, in order to ensure the blood supply to the body, the heart rate will be accelerated, resulting in a fast and weak pulse. There are many reasons for a fast and weak pulse, so it is recommended to go to the hospital in time to find out the cause and get timely treatment.