Background Infants with single ventricle physiology are desaturated with arterial saturations consistently between 75-85%. Home monitoring with daily pulse oximtery improves interstage survival in these patients. Patients are typically sent home with expensive, bulky hospital grade pulseoximeters. Relatively inexpensive, portable devices equipped with Bluetooth technology are now available. For outpatient monitoring, these would be more convenient for families and more efficiently transmit information to physicians. However, these devices have not been validated in this patient population, although many of them are FDA approved for use in children. This study evaluates the accuracy of one portable pulse oximeter in these hypoxemic infants. Methods Twenty-four infants under 12 months of age with baseline oxygen saturation less than 90% secondary to cyanotic congenital heart disease were included in this study. Pulse oximetry with WristOx2 3150 with infant sensors 8008J (study device) and Masimo LCNS saturation sensor connected to Philips monitor (hospital device) were measured simultaneously and compared to arterial oxy-hemoglobin saturation measured by co-oximetry. Statistical analysis with Schuirmann’s TOST equivalence tests, were performed to evaluate the performance of both the hospital and study pulse oximeter devices and compared to co-oximetry, with equivalence defined as an absolute difference of 5% saturation. The differences between study sensor bias and hospital sensor bias were evaluated with a signed rank test. Results For the 24 infants, average age was 13 days, (range 2 to 195) and average saturation by co-oximetry was 72%. Neither study nor hospital device met the predefined standard for equivalence. The study device reading was on average 4.0% higher than the co-oximeter (90% confidence interval 2.3-5.7%). Due to this confidence interval crossing 5%, it does not meet the predefined standard for equivalence (p=0.16). On average the hospital device was 7.4% higher than the cooximeter (90% CI 5.4-9.5), and also did not meet the predefined standard for equivalence (p=0.97, Figure 1b). 54% of the study device sensor readings and 38% of hospital device sensor values were within 5% points of the cooximeter measurements. Conclusion Both the study and the hospital device tended to overestimate oxygen saturation in this patient population when compared to gold standard co-oximetry. The study device had less bias from co-oximetry compared to the hospital device. Hence we conclude that the study device is at least as accurate as the hospital device and offers the advantage of being more portable and with blue tooth technology that allows reliable, efficient data transmission for home monitoring. A larger study would be needed to determine if the study device is more accurate than the hospital device. Whether devices that more accurately measure peripheral saturations will lead to better neurodevelopmental outcomes in addition to survival is also an area of further study. This study shows that there is significant bias when using either pulse oximeters for these hypoxemic infants, highlighting the need for further improvements in pulse oximetry design for this specific population.