Accusative case with inanimate nouns in the plural
Hello! Do you mean animate nouns in Accusative case? The inanimate nouns in the Accusative case coincide with the Nominative plural:
Я вижу книги. I see the books.
Я беру стаканы. I take the glasses.
The Accusative animate plural coincides with the Genitive plural. There are many different endings, there is a special table, you can have a look at it here: http://www.russianforfree.com/grammar-of-russian-nouns-genitive.php
In the case of "героев", the Nominative singular ends in й, so, according to the table, the ending in the Accusative animate plural and Genitive plural is going to be ев.
In the case of люди-людей it is an exception, it has to be memorized,