Tachycardia is defined as a heartbeat greater than 100 beats per minute. There are various types of tachycardia, depending on where they originate.
Sinus tachycardia is completly harmless, it's just your heart beating normal, only fast.. I have IST, or inappropriate sinus tachycardia. It basically means that my heart is easily stimulated. I have a high resting heart rate, usually between 85 and 95, (when I sleep it falls