Who vs. Whom

So here I am editing away this morning when I come across the following sentence:

Matt deserved to know the truth, seeing it was no-man’s hour and here he was driving me across town, tracking a man who’s name brought a ripple of fear to those who heard it.

(I know, it's a bit of a long sentence. Generally I have a tendency to write concise, snappy ones - this sentence is the exception.)

So what should it be? Those "who" heard it? Or those "whom" heard it. When in doubt, I check out Encarta - I LOVE their dictionary. But this morning their explanation of Who vs. Whom still left me confused.

So my next stop was Grammar Girl - who's tips have helped me loads of times - today was no exception. Grammar Girl gave a quick and dirty tip to help sort it out:

Like whom, the pronoun him ends with m. When you're trying to decide whether to use who or whom, ask yourself if the answer to the question would be he or him. That's the trick: if you can answer the question being asked with him, then use whom, and it's easy to remember because they both end with m.

For example, if you're trying to ask, "Who (or whom) do you love?" The answer would be "I love him." Him ends with an m, so you know to use whom.

Okay, so I think I got this. So in this case it would be "Who (or whom) heard it." The answer would be "He heard it." There's no m in he so you know to use who.

Someone correct me if I'm wrong here.... =)