Back in the late 70's or early 80's I read a romance novel set in the late 17th or 18th century in England I think. The characters were Alex and Elysa. He had dark hair and she had red hair & green eyes. He was rich, she was poor and I think he helped out of a situation and brought her to his manor/estate. He seduces and then uses that as leverage to make her marry to marry him. Eventually of course they fell in love. I thought the title was maybe Untamed Heart or The Wildest Heart. The book cover was a picture of a woman on a running horse. She had long, flowing fiery red hair and wearing a green dress I think. I've searched the web and haven't been able to come up with anything. It was the first romance novel I ever read and I would love to find it. Any help would be appreciated!