Accusative of the word "prase" is "prase", so they both are. There are different ways to declinate words.
"prase" is neuter, paradigm "srdce" (unless I'm mistaken), while "kráva" is female, paradigm "žena".
TL/DR:They are both in correct accusative forms.
You're correct, only the declension pattern used for "prase" is "kuře". And the word "srdce" uses pattern "moře". There are two neuter patterns ending with "e" in the nominative singular. Czechs look at the genitive singular of these nouns to see to which pattern group they belong. (Of the two patterns, animals usually belong under pattern kuře.)