I wanted to post this because I found it while I was looking up the "S3" that Steph mentioned. It is called a "gallop rythym." This website explains that the S3 has the syllables of "ken-tuc-ky." It has a .wav file that you can download and listen to. I listened to it over and over again and cannot hear the S3 or the extra syllable there. I guess if you listen to heartbeats all day long...
If you follow this link instead, there is a list for 4 examples of S3 and the S4 rythyms (I had no idea such a thing existed). http://www.childrenshospital.org/cfapps/mml/index.cfm?CAT=subtopic&SUBTOPIC_ID=1101
By the way, the S4 has the cadence of the syllables "ten-nes-see," and that one is a little easier to distinguish.
As for information about the significance of the gallop rythym with HLHS, I couldn't find a thing on it at all. It just another example of Jaden's way of being extra special I guess!
Edited to add: Did you know that 80% of pregnant women have an S3? Hmmm... This website has some great information: http://www.chfpatients.com/faq/s3s4.htm