What does tachycardia mean in medical terminology?

Tachycardia means an abnormally fast heart rate, defined as a resting heart rate above 100 beats per minute in adults. The term breaks down into tachy meaning fast and cardia meaning heart condition. Tachycardia can be caused by exercise, fever, anxiety, dehydration, anemia, hyperthyroidism, or cardiac arrhythmias. Types include sinus tachycardia where the heart's normal pacemaker fires too fast, supraventricular tachycardia originating above the ventricles, and ventricular tachycardia originating in the ventricles which can be life-threatening.