The reasons for rapid heartbeat in advanced cancer include: 1. lung causes: tumor invades the lung, or originates in the lung, resulting in decreased pulmonary ventilation and faster heartbeat under hypoxic condition; 2. heart causes: tumor compression or other reasons, requiring faster heartbeat in order to provide more nutrition to the body; 3. anemia: decreased hemoglobin content in the blood; 4. other combined causes, such as tumor compression, ascites, increased pressure in the abdominal cavity, compressing the heart, squeezing the lungs, tumor in the mediastinum squeezing the trachea, etc.