Cardiovascular Analysis of PEM

The purpose of this study is to examine cardiopulmonary function in Chronic Fatigue Syndrome (CFS) patients and determine how it relates to the common symptom of Post-exertional malaise (PEM). Subjects will complete a maximal exercise test on 2 subsequent days. Total blood volume will be measured prior to each exercise test, and patient with hypovolemia on day 1, will be randomized to either a saline or sham infusion prior to the 2nd exercise test. A total of 80 CFS patients will be enrolled.