The aim of the current study is to describe the long-term clinical and hemodynamic characteristics of adult patients with single-ventricle physiology who have not undergone the Fontan operation and consequently have remained cyanotic. Adult patients at the Ahmanson/UCLA Adult Congenital Heart Disease Center with non-Fontan single-ventricle physiology who had undergone cardiac catheterization between 2005 and 2011 were included. Echocardiographic and cardiac catheterization data were reviewed. Mean estimated single ejection fraction was 56 ± 8%. Eight of 13 subjects had documented E/E' data with a mean of 6.44. Seven subjects had both A' and E' data documented, of which two subjects exhibited A' > E'. Mean ventricular end-diastolic pressure (MVEDP) was 15.77 ± 4.91 mm Hg, and was >12 mm Hg in eight of the 13 patients (62%). MVEDP was also analyzed by age, and in the single-ventricle patients was 13.55 ± 4.12 mm Hg in those <50 years of age, compared with 20.75 ± 1.89 mm Hg in those >50 years of age (P = .003). MVEDP prior to inhaled pulmonary vasodilator administration was 14.75 ± 5.5 mm Hg, compared to 15.00 ± 6.78 mm Hg in the postvasodilator group (P = .48). Subjects with end-diastolic pressure (EDP) <12 had a mean brain natriuretic peptide (BNP) of 108 ± 197 pg/mL, while subjects with EDP >12 had a mean BNP of 234.5 ± 127.36 pg/mL (P = .11). Cyanotic adult single-ventricle patients not palliated with Fontan completion have preserved single-ventricle systolic function but develop elevated ventricular filling pressure with increasing age. Only invasive hemodynamic measurements demonstrated elevated ventricular filling pressures, while traditional echo/Doppler criteria for diastolic dysfunction were not met. Aging with cyanotic single-ventricle physiology is associated with a greater degree of filling pressure elevations than in the general population. Single-ventricle patients with EDP >12 exhibited markedly elevated BNP compared to those with normal EDP.