When the blood calcium concentration is ≥2.75 mol/L, it is called high blood calcium. Chronic high blood calcium causes enhanced myocardial contractility and accelerates the repolarization process of the myocardium. There are several main reasons for high blood calcium: 1. parathyroid hormone-dependent hypercalcemia, which can be seen in hyperparathyroidism, familial hypocalcemic hypercalcemia, and lithium poisoning. 2. non-parathyroid hormone dependent hypercalcemia, seen in vitamin D toxicity, malignancy, sarcoidosis and nodular disease, lactoblastic syndrome, pheochromocytoma, use of thiazide diuretics, and activity restriction. 3. Rheumatic diseases. 4. Certain endocrine diseases. The causes of increased blood calcium are complex, and patients with this condition should go to the hospital in time to improve the relevant examinations to clarify the causes.