I don't think the Ah really matters here except that it gives you about one extra out in the form of the backdoor draw. We know that he actually limp-called with 79s; clearly he's quite likely to be in there with two hearts, whether or not one of them is an ace, and he could easily make this play with 7h5h, Jh9h, Qh9h, Kh9h, or JhQh. In fact *I* would make this play with many of those hands, and I'm not all that LAggy.