Can heartburn pain vary in intensity?

Earlier this week, one of my wife's friends told her that she started having severe chest pains one evening earlier this month. She said that the chest pain was so bad that that she thought she was having a heart attack. She went to the Emergency Room, and the doctors ran a bunch of tests. Her heart was fine, and she was told that her chest pains was most likely "severe heartburn." My wife's friend, who's in her late 20s, never had heartburn before that night, and has had no problems since then either.

My wife and I were really surprised when her friend told us what happened. Both of us are in our early 30s, and we each get heartburn at least a few times each year since we've been in our mid 20s. Neither one of us have ever had heartburn pain so bad that we thought that it could be something more serious. On the flip side, neither of us have ever had a "mild" case of heartburn where the pain is not as bad as it usually is.

Is it possible for heartburn pain to vary in intensity? Can the pain ever be so severe that it could be mistaken for a heart attack? Are there any factors that can cause the pain to be particularly severe?

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