The typical rate range for sinus tachycardia is from 100 to over 200 beats per minute. The peak heart rate that can be achieved is inversely related to age and is usually no more than 220 minus the patient's age. Each P is followed by a QRS and viceversa. The Ps are constant in morphology and upright in lead II. The PR interval typically shortens with increasing heart rate. Sinus tachycardia is a physiologic response to a variety of stimuli including exercise, anxiety, fever, hyperthyroidism and drugs such as epinephrine. The following animation illustrates what we have just described.