Tachycardia is caused by something that disrupts the normal electrical impulses that control the rate of your heart's pumping action. Many things can cause or contribute to problems with the heart's electrical system. These factors include: Damage to heart tissues from heart disease Abnormal electrical pathways in the heart present at birth (congenital) Disease or congenital abnormality of the heart Anemia Exercise Sudden stress, such as fright High blood pressure Smoking Fever Drinking too much alcohol Drinking too many caffeinated beverages Medication side effects Abuse of recreational drugs, such as cocaine Imbalance of electrolytes, mineral-related substances necessary for conducting electrical impulses Overactive thyroid (hyperthyroidism) In some cases, the exact cause of tachycardia can't be determined.