Per here: http://www.w3.org/TR/html401/struct/global.html#h-7.5.4
%flow element which display as a block (in this case <h1>) always should surround %inline elements (such as <a>).
Another example <div> should always be outside <span>.
That is to say:
<h1><a href="#">heading</a></h1>
is correct.
An even easier way of under standing this is that the following makes sense:
<h1><a href="#1">my link</a> and <a href="#2">my other link</a></h1>
It would be highly unusual to try the inverse with multiple <h1>s inside an <a>.