Postural orthostatic tachycardia syndrome (POTS) describes a form of orthostatic intolerance characterized by chronic fatigue, tachycardia (more than 40 beats per minute over baseline in patients 13 years of age and younger or more than 120 beats per minute for patients 14 years of age and older) typically without hypotension upon standing POTS is commonly seen in teenage girls and manifests as palpitations, dizziness, and tremulousness The diagnosis may be made when no other cause for symptoms is found and the patient has replication of symptoms with headup tilt table testing Management consists of a multidisciplinary approach including family education, avoidance of precipitating factors (e.g., sudden posture changes, large meals, or vasodilating drugs), adequate water and salt intake, and regular exercise Medications targeted at maintaining blood volume, avoiding vasodilation, or treating secondary symptoms may be required Sinus Bradycardia Low basal metabolic rate associated with hypothyroidism may present with a slow HR and sinus rhythm Similarly, in the absence of significant sympathetic nervous system input, the HR may be slow This state may be responsible for the sinus bradycardia associated with sleep or with ingestion of drugs such as clonidine, sedative-hypnotics, or narcotics Athletic training may result in a highly efficient heart with high ventricular ejection fraction and sinus bradycardia