Sinus tachycardia: Fast heartbeat (tachycardia) that occurs because of overly rapid firing by the sinoatrial node. Sinus tachycardia is usually a rapid contraction of a normal heart in response to a condition, drug, or disease, such as pain, fever, excessive thyroid hormone, exertion, excitement, low blood oxygen level (hypoxia), or stimulant drugs, such as caffeine, cocaine, and amphetamines. However, in some cases sinus tachycardia can be a sign of heart failure, heart valve disease, or other
illness.
