Fish fits well in a healthy diet since it replaces red meat, which has a heavy load of saturated fat. But fish may go farther than that. A certain type of fat in fish oil (omega-3 fatty acids) may actually be good for the heart.
Heredity does not account for this - Eskimos who migrate to other countries eventually assume the same coronary risk as their new compatriots. One study, for example, demonstrated that Eskimos who move to Denmark develop coronary disease at the same rate as Danes - more than 10 times the rate of Eskimos in Greenland.
Instead, the explanation appears to lie in the native diet: Eskimos typically consume just as much fat as Danes do, but in Greenland that fat comes entirely from the sea. In Denmark, on the other hand, dietary fat comes primarily from land animals, much as it does in the U.S.