Why does heathcliff resemble a hero in a romantic novel in wuthering heights?

Because he is a child of nature (wild hair, rebellious, untamable spirit). He was modeled on Lord Byron, whom all the Brontes were fascinated with and is "mad, bad, and dangerous to know". He is Romantic in the sense that he is brooding and dark (contrast him with Cathy's other suitor), passionate and so deeply in love with one woman that it consumes him.