Background: The function of the right ventricle (RV) is difficult to evaluate by 2-dimensional echocardiography because it has more complex geometry and function than the left ventricle. The aim of our study was to evaluate right ventricular (RV) systolic function in the neonate using newly developed single beat 3-dimensional echocardiography (sb3DE). Method and Results: We enrolled 15 healthy or premature neonates (0 to 53 days after birth). We scanned one beat full volume using Siemens ACUSON SC2000 (Siemens AG) echocardiography with 4Z1c Full Volume transducer without ECG-gating. RV end-diastolic (RVEDV) and systolic volume (RVESV) were computed with special software dedicated to analysis for RV volume. RV ejection fraction (RVEF) and RV stroke volume (3D-RVSV) were also calculated. While RV stroke volume was also determined from the recordings of ejection blood flow velocity and diameter at the level of the pulmonary orifice in the RV outflow tract (Doppler-RVSV). Tricuspid annular plane systolic excursion (TAPSE) was also measured by 2D echocardiography. Results: It took 15 minutes for total acquisition of echo data including one beat full volume and 4 - 5 minutes to compute for RVEDV and RVESV. Full volume data were obtained successfully in all cases with average volume rate of 60 volumes / sec. RVEDV ranged from 5.1 to 10.7 ml (average 7.5 ml), RVESV ranged from 2.3 to 5.8 ml (average 3.9 ml). There was a good correlation between 3D-RVSV and Doppler-RVSV (r = 0.77). Bland-Altman plots revealed that 3D-RVSV was underestimated by an average of 1.78 ml compared to Doppler-RVSV. TAPSE positively correlated with 3D-RVEF (r = 0.58, P = 0.038). Conclusions: Newly developed sb3DE enables us to perform 3-dimensional acquisition of RV volume without ECG-gating even in neonate. However, 3D-RVSV currently tends to be underestimated in the neonatal measurement.