What's so ironic about the Scottish Heavy Ale? Mostly that it's not exactly what you'd call heavy - it's actually one of the lighter beers you'll find, at least in terms of gravity. Everything is relative, though, so it's worth noting that there are differences between this style and its close relative, the Scottish Light Ale.
While the Heavy may not be heavy in comparison to…well, almost anything else, it is heavier than the sixty-shilling light ales of Scotland. To the extent that we care about differences between beers and how those beers are produced, that's really all that matters!
But Scottish Heavy is definitely a style that requires a deft hand, and nailing the "heavier" but still "Scottish session ale" elements is important. There's more to this beer than taking your Scottish Light recipe and adding a few more gravity points.