A heartbeat between 60 and 100 beats per minute is considered sinus rhythm, below 60 beats per minute is considered bradycardia, and above 100 beats per minute is considered tachycardia. Bradycardia is often seen in patients with hypothyroidism and in some patients with sinus node hypofunction, which requires a thyroid function test and esophageal pacing to clarify the diagnosis. In addition, some anti-arrhythmic drugs, including cortisone and mexiletine, can cause bradycardia, which can be recovered after stopping or reducing the dosage. In addition, beta-blockers among antihypertensive drugs, including betalactam and Conotene, can also cause bradycardia, which can be recovered after stopping or reducing the dosage. Tachycardia is usually seen after strenuous activity or stress or anxiety, and is often seen in various types of tachyarrhythmias, including supraventricular tachycardia, ventricular tachycardia, rapid atrial fibrillation, and various types of premature beats.