Objectives The gold standard to obtain pressure-volume relations (PVR) of the heart, the conductance technology (PVR.sub.Cond ), is rarely used in children. PVR can also be obtained by 3D-echocardiography volume data combined with simultaneously measured pressure data by a mini pressure-wire (PVR.sub.3DE). We sought to investigate the feasibility of both methods in patients with univentricular hearts and to compare them, including hemodynamic changes. Methods We studied 19 patients (age 2-29 years). PVR.sub.3DE and PVR.sub.Cond were assessed under baseline conditions and stimulation with dobutamine. Results Obtaining PVR.sub.3DE was successful in all patients. Obtaining PVR.sub.Cond was possible in 15 patients during baseline (79%) and in 12 patients under dobutamine (63%). Both methods showed that end-systolic elastance (Ees) and arterial elastance (Ea) increased under dobutamine and that Tau showed a statistically significant decrease. Intraclass correlation (95% confidence interval) showed moderate to good agreement between methods: Ees: 0.873 (0.711-0.945), Ea: 0.709 (0.336-0.873), Tau: 0.867 (0.697-0.942). Bland-Altman analyses showed an acceptable bias with wider limits of agreement: Ees: 1.63 mmHg/ml (-3.83-7.08 mmHg/ml), Ea: 0.53 mmHg/ml (-5.23-6.28 mmHg/ml), Tau: -0,76 ms (-10.73-9.21 ms). Conclusion Changes of PVR-specific parameters under dobutamine stimulation were reflected in the same way by both methods. However, the absolute values for these parameters could vary between methods and, therefore, methods are not interchangeable. Obtaining PVR.sub.3DE in a single ventricle was easier, faster and more successful than PVR.sub.Cond . PVR.sub.3DE provides a promising and needed alternative to the conductance technology for the assessment of cardiac function in univentricular hearts.