I disagree with P Diddy about Mayo. Don't know much about Wash U. I'm also interested in cardiology and Mayo is high on my rank list. Mayo has matched people over the past few years at Mayo, Barnes-Jewish (WashU), Texas Heart, Cleveland Clinic, Cornell, Emory, Hopkins, William Beaumont, etc. Among the top 15 ranked cardio programs per US News, Mayo residents have historically at 8, including all of the top 3. I admit that they may not be as likely to match at MGH, BWH, etc. but I would say that Mayo's list is probably stronger nationally than UCLA and many other programs that may be much harder to get into (usually because of people competing over being in a nice location like NYC).
My feeling is that you need to take Mayo's info with a grain of salt. First, they have many international medical grads with amazing credentials. These people might have a harder time matching in cardiology than US grads (I'm not sure if difficulties are the same for them at the fellowship level).
Also, Mayo gets strong people from all over the country. I spoke to a few of the residents, and they seemed to include a combination of some who came to Mayo for the Mayo experience and for the training but who wanted to return home after finishing up and some who are looking for bigger things in academic medicine and care more about the name and reputation of their program.