My experience was different. There were several female applicants from my residency program, and we got the same (or maybe less, in the case of one of the people) vs. male applicants, given similar stats and publications. If you look at the acceptance rates for male and female applicants, they are very very similar (haven't seen the data for last year's match, but I did for the one a couple of years ago). If there was as much bias as you all state, the match rate for female applicants should be >> that for male applicants. I also would argue that women who apply to cardiology are a self-selected group willing to go to great lengths to get the fellowship (not that it's not a hard one to get for anyone, male or female) and I think there were several qualified women in my residency who opted out of cardiology either because they didn't want the lifestyle, or because they were discouraged from doing cardiology.
I also feel like a I got "hard balled" at a couple of interviews (though not most of them) by older male attendings who asked a lot of questions about whether I was married and had kids, or wanted any kids, etc. I really doubt all the guys at the same interview got a similar grilling.
I think there is disagreement among cardiology faculty about whether it is good to recruit female applicants vs. not. Some would like to have as few women as possible (and perhaps will try to keep us out of their particular programs), some don't care either way, and some feel that they want to recruit women (perhaps even preferentially). Most I think don't care...so I disagree that there is systematic "affirmative action" going on at a systems level, and I didn't see any evidence of that.
I think when people don't get all the cardiology fellowship interview invites they want, they start wondering why. It happened to me, and I think it happens to most all other applicants. The truth is that a lot of the applicants are similar, both on paper and in terms of strength of letters of recommendation, and it turns out to be tiny reasons (or no reason, really, in a lot of cases) that determines why one applicant gets an interview at a particular place, and another one does not.
A lot of people don't get a lot of interviews, or do get interviews but then don't match in cardiology. It happened to me, and for no apparent/obvious reason. I generally don't act like a troll at interviews, had high USMLE scores, decent LOR's (not from famous people, but decent), 1 real publication and a couple of wimpy ones (i.e. poster presentations, etc.) and was from a well pretty good university IM program.