A computational model of a planar, phased array transducer is developed to aid in the design of an high intensity, focused ultrasound transducer for the non-invasive treatment of congenital heart disease in newborns. The aim is to predict the size, shape and temperature of the high-intensity focal region, and acoustic artifacts surrounding the focal area, created by a transducer. Acoustic intensity fields are calculated and mapped by numerically integrating a form of the Rayleigh-Sommerfeld integral. The resulting temperature field is predicted by the Pennes bio-heat transfer equation by implementing a 3-dimensional finite difference method algorithm. Based on the metrics of an atrial septal defect and the metrics of isolated patent ductus arteriosis in consecutive human neonates, a first iteration of an array design has been performed. A random-sparse array configuration is used to reduce side-lobe and grating lobe effects. To avoid the scattering and reflecting effects of ribs, the transducer is configured to fit in the gaps between the ribs. The three arrays are phased act cooperatively as a single array. Each array contains 45 elements (3 x 15), with every third element active (45 total). The transducer was designed to have a center frequency of 1.2 MHz. A first iteration design was fabricated using PZT-8 piezoelectric ceramic. The exposimetry of the transducer was captured and compared to numerical models. The exposimetry results correspond well with the numerical models, warranting further development of the transducer design.