Inappropriate sinus tachycardia (IST) is an uncommon form of arrhythmia which is characterized by an exaggerated increase in heart rate that is out of proportion to normal physiologic demands. Usually, IST is triggered by orthostasis, minimal exertion, and psychological stress. The etiology of IST remains ill-defined. However, proposed mechanisms include: enhanced sinus node automaticity, alterations in autonomic function associated with increased sympathetic activity or reduced parasympathetic activity, and impaired baroreflex control. Recently, increased levels of autoantibodies to beta-adrenergic receptors have been observed in patients with IST. The clinical presentation of IST is highly varied and ranges from short episodes of palpitations associated with dyspnea, atypical precordial pain, cephalalgia, fatigue, and occasional syncope and presyncope to incapacitating incessant tachycardia. In general, IST is a diagnosis of exclusion. It is important that other causes of sinus tachycardia are excluded before making a diagnosis. Evaluation of autonomic function is essential for a diagnosis of IST. Treatment of IST is based on autonomic function findings and involves multidisciplinary management, including cardiac rehabilitation. Control and restitution of normal autonomic function is essential. The prognosis is benign though regular follow-up is required to optimize therapy.