A heat sink (100) includes a cooling block (105) having a plurality of fins (110) extending through the block to provide a series of coolant channels (112) extending between the fins, the channels having in the interior of the block a venturi narrowing. Beneficially, the channels have coolant entry regions in at least two different regions (115, 120) of the block to direct a plurality of coolant flows into the interior of the block from different directions.