Gobbledegook

'Pregnancy heart risk' says The Star(site under redevelopment); 'Mums in heart attack risk' as The Sun has it; 'Pregnant women 'four times as likely to have a heart attack' for The Daily Telegraph (note the quote marks for something that is being said for the first time. By The Daily Telegraph). The NHS's Behind The Headlines service has a better analysis of the science behind the study than I can offer, so go there for that.
What I can add is only this: the press release associated with the study states

Although acute myocardial infarction (AMI) is rare in women of child-bearing age, pregnancy can increase a woman's risk of heart attack 3- to 4-fold, according to a study published in the July 15, 2008, issue of the Journal of the American College of Cardiology.

The journal issue containing the study is still embargoed meaning I haven't been able to read the full text, so they may well use just that sentence, and report just that finding. What's interesting, though, is another study, from 2006, and published in Circulation whose abstract states:

Although acute myocardial infarction is a rare event in women of reproductive age, pregnancy increases the risk 3- to 4-fold.

Eerily similar, eh. As the Behind the Headlines piece explains, the current study wasn't comparative, so no relative risk increase can be inferred. They also report that the authors note that other studies have found a 3 to 4 fold increase in risk (that's our friends from 2006 then). So...the headlines, the story, the new findings et cet et cet, are all based on a line copied and pasted by a PR person from the abstract of a 2006 study and nothing to do with this one. I've heard rumours that Germany has invaded Poland - I wonder when the papers will pick up on it.