A west-to-east traverse of 24 heat flow measurements was made across the Caribbean Sea floor from the eastern Venezuelan basin to 80 km east of the Lesser Antilles arc crest. The resulting heat flow profile includes an increase from basin values in the eastern Venezuelan basin and a zone of high values extending the length of the transect. Superimposed on this zone are two heat flow peaks containing maximum values, one at the Aves swell and the other at the Lesser Antilles arc. Based on 21 acceptable values, average heat flows were 1.87 heat flow units (1 HFU=1 μcal cm-2s-1) (8 values) for basin regions, 3.63 HFU (9 values) for the Aves swell peak, and 4.16 HFU (4 values) for the Lesser Antilles are peak. High heat flow is expected for the Lesser Antilles arc, the present site of seismic and volcanic activity associated with subduction of the North American plate at the West Indies trench. The heat flow peak at the Aves swell agrees with an island arc formation for this presently inactive feature, with its high heat flow anomaly attributed to radiogenic heat sources concentrated during subduction in the past. Both the Aves swell and the Lesser Antilles arc are believed to be heated by radiogenic sources accumulated during past subduction, but only the Lesser Antilles arc is now receiving new heat from mechanical processes directly coupled to active underthrusting. This suggests that differences in the two heat flow peaks at the Aves swell and Lesser Antilles arc reflect the relative importance of different heat-producing mechanisms at island arcs.