The article provides information about postural orthostatic tachycardia syndrome, a condition of orthostatic intolerance associated with excessive heart rate increments upon upright posture, and other heterogeneous group of disorders that share similar characteristics. Orthostatic intolerance is defined as the development of symptoms on standing and the failure of the body to adjust on an upright position which can be relieved through lying face upward. Among the usual complaints of patients with orthostatic intolerance include palpitations, exercise intolerance fatigue, light-headedness, tremor, headache, nausea, near syncope and syncope.