Effects of Escitalopram on Autonomic Reactivity in Post Traumatic Stress Disorder

Inclusion Criteria: * Inclusion Criteria - Group I * Patients, men and women between 19 and 55 years of age, inclusive. * Patients with diagnosis of Posttraumatic Stress Disorder as determined by Mini-International Neuropsychiatric Interview (M.I.N.I.). * Patients, who are able to comprehend and satisfactorily comply with protocol requirements and have an ability to read and write English. * Patients, who signed the written informed consent given prior to entering any study procedure. * Inclusion Criteria - Group II * Patients, men and women between 19 and 55 years of age, inclusive. * Patients with diagnosis of Major Depression as determined by Mini-International Neuropsychiatric Interview (M.I.N.I.). A diagnosis of PTSD will be exclusionary. * Patients, who are able to comprehend and satisfactorily comply with protocol requirements and have an ability to read and write English. * Patients, who signed the written informed consent given prior to entering any study procedure. Exclusion Criteria: * History of cardiovascular disease or a history of hypertension. * Patients with a concurrent Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnosis in any of the following categories as determined by the M.I.N.I. * Lifetime Schizophrenia and Schizoaffective Disorder * Lifetime Bipolar I Disorder * Substance Dependence or Abuse (excluding nicotine) within one month prior to the Screening Visit. * Patients with a history of intolerance or hypersensitivity to escitalopram or citalopram. * Patients who based on history or mental status examination have a significant risk of committing suicide. Current suicide risk (past month) will be assessed using the M.I.N.I. Suicidality Module. Subjects considered at high suicide risk based on the module (\> 17 points) will be excluded from study participation. * Patients who are homicidal or violent and who are in the Investigator's opinion in significant imminent risk of hurting others. * Subjects will be excluded who have a history of significant medical illness and who are on medications that affect cardiac and/or autonomic function. * Female patients who are pregnant, planning to become pregnant, or if of childbearing potential, not using an acceptable method of birth control.