An intercooler for an internal combustion engine has a fin-and-tube block including a plurality of flat heat transfer units having internal fluid passages orientated transversely to the direction of air flow, and arranged parallel to one another to define gaps therebetween. Fin units are disposed in the gaps and contact adjacent heat transfer units. Each fin unit defines a longitudinally-oriented air flow passage, the air flow passages having a first air flow area at an air inlet end and a second air flow area at an air outlet end, the first air flow area greater than the second air flow area. The fins of the fin units converge in the direction of the air flow through the passage so that the pitch of the fins at the air inlet end of is greater than the pitch of the fins at the air outlet end.