Adults with cyanotic congenital heart disease have elevated levels of plasma proatrial natruretic peptide (proANP) which most likely results in chronic dehydration, leading to reduced oxygen transport to tissues and shortness of breath with activity. The purpose of this study is to characterize adults with cyanotic congenital heart defects with respect to their body composition (water and fat-free mass) and resting metabolic rates. The study consists of several measures of how much body water, fat and lean tissue a subject has, and measures the number of calories the subject's body uses at rest. Adult subjects with cyanotic congenital heart disease will be recruited along with healthy noncyanotic control subjects matched for age, gender, and body weight.