The Penn State pediatric ventricular assist device (PVAD) was designed as a bridge-to-transplant device for children on the heart transplant waiting list, but thrombus formation on the polyurethane urea blood sac remains an issue. After PVAD ovine studies, blood sacs were evaluated using immunofluorescence and confocal microscopy, environmental scanning electron microscopy (ESEM), and optical profilometry (OP). These data were correlated, demonstrating that areas of higher surface roughness could facilitate deposition of platelets and fibrin.