Tachycardia refers to a phenomenon where the heart rate exceeds 100 beats per minute. There are many diseases that can cause tachycardia, with the most common ones including: First, heart diseases such as congenital heart disease, cardiomyopathy, and coronary artery disease can lead to heart failure, often resulting in tachycardia; Second, respiratory diseases, such as chronic obstructive pulmonary disease (COPD) or cor pulmonale, can also lead to tachycardia due to long-term oxygen deficiency; Third, endocrine disorders, such as hyperthyroidism, often cause tachycardia; Fourth, hematological disorders, such as severe anemia, often lead to tachycardia as well; Additionally, fever can also cause tachycardia.