This study presents computational results in a complex three-dimensional louver geometry. The three-dimensionality occurs along the height of the fin, where the angled louver transitions to the flat landing and joins with the tube surface. The transition region is characterized by a swept leading edge and decreasing flow area between louvers. The results show that for Re-b = 1100, the flow on the angled louver is dominated by spanwise vortex shedding, which is weakly three-dimensional. On the other hand, the flow in the transition region exhibits strong three-dimensionality. A high-energy compact vortex jet forms in the vicinity of the louver junction with the flat landing and is drawn under the louver. The top surface experiences large velocities in the vicinity of the surface and exhibits high heat transfer coefficients. Although the flow slows down at the flat landing, the large induced velocities on the top surface increases the heat transfer coefficient on the tube surface.