Introduction: The patent ductus arteriosus (PDA) is a common lesion in infants. Two-dimensional echocardiography (2DE) is standard for PDA imaging. Three-dimensional echocardiography (3DE) is often used for complex anatomy and for procedural planning. Very limited data exist on use of 3DE of the PDA in infants despite its value in planning interventions. We aim to determine the agreement between 2DE and 3DE in measuring PDAs in infants. Hypothesis: Significant agreement exists between 2DE and 3DE for PDA measurements. Methods: Infants with a known PDA underwent 2DE and 3DE imaging by an IRB-approved protocol. Subjects were <1 year old, >32 weeks corrected gestation (CGA), >1kg, and clinically stable. Parasternal short axis (PSAX) and suprasternal notch (SSN) PDA images were taken. Two blinded observers measured the pulmonic (PA) and aortic (Ao) end of the PDA. Interobserver variability was assessed by interclass correlation (ICC), Bland-Altman (BA), and coefficient of variability (COA). 2DE to 3DE agreement was assessed by BA. Results: For 19 subjects acquired, median CGA 38.0 weeks (IQR 35.6-39.1), median weight 3.07kg (IQR 2.83-4.34). ICC for 2DE and 3DE in all views was >0.98 with narrow limits of agreement (LOA) (Table 1). BA showed low bias and narrow LOA. COA was <3.6%. Paired 2DE-3DE comparison had low bias and narrow LOA (Table 2). Conclusions: PDA measures by 2DE and 3DE have strong interobserver agreement. Paired 2DE-3DE measures show low bias and variability. A larger cohort will test agreement with variable subject size, ductal size & type, and compare to angiography. Preliminary data show promise for 3DE in future use for PDA procedural planning.