We estimate the seismic structure of the slow spreading Lucky Strike segment of the Mid-Atlantic Ridge, located approximately 300 km south of the Azores platform, using seismic reflection and seismic refraction data acquired in June 2005 as a part of the Seismic Study for Monitoring of the Mid-Atlantic Ridge (SISMOMAR) survey. The three-dimensional velocity model shows an upper crustal low-velocity anomaly running parallel to the ridge axis, which is limited by the median valley bounding faults. The velocity models also show a low-velocity anomaly underlying the axial melt lens reflector located at the segment center below the Lucky Strike volcano. This lower crustal low-velocity region can be explained by elevated temperatures and possibly small amounts of melt. The lower crustal low-velocity anomaly and the axial melt lens reflector constrain the geometry of the magma chamber responsible for the construction of the Lucky Strike volcano. The presence of this magma chamber and thick crust at the segment center are consistent with a focused melt supply to the segment center.