I lied at MEPS. Will they go back and look through my medical records?

I would not worry about it right now.

Let the doctors do what they do.

The Doctors are going to say yes or no.

Lol when you get that security clearance they will find out

I would say since, your label is "potential recriut", that you have not signed the contract. Be aware that once you sign the contract, actions like this could place you into a situation where you could be charged for falsifying government documents. I would also add that you need to seriously reconsider your morals. A, you are lying and b, if you are lying to gain a benefit; neither of these morals are in alignment with morals required of Soldiers. Since you felt the need to admit to lying on an open website, that is easily found, understand now what azimuth check means. Are you on the right path in life to join an organization where people's lives can potentially be dependant on your willingness to place others before yourself?

As a former Recruiter, if there is no proof that something was said or done, then you don't need to document it. That being Said, at the Age of Six, not everyone can remember what they were told, so you may have misheard the doctor.
the MEPS station doesn't have the time, to request everyone's Medical Records, unless there is a Problem that you tell them about.
If your Current Civilian Doctor tells you that you have no heart murmur at this time, then you would have no problem and could document it on your enlistment contract if you want or not.
If the Doctor who found it, was at the MEPS station, and he says it's no big deal, then document it as required and move on.

Probably not do bc anything at all, but Today’s Military is a lot different than when I was in, did your Recruiter tell you not to B mention this problem? I knew a few that would have just to make their quota

The possibility that the heart murmur is not present as an adult, happens sometimes. The defect in your heart can spontaneously heal itself in some cases. You may be lucky in that matter.

I will just state my feeling as a medical professional on the biggest matter I see. Not trying to make anyone mad, but there is a MUCH bigger problem in this case. The biggest problem, as I see it, is that you have a baseline dishonesty in you that may cause bigger problems. This problem may not effect you directly but could have a staggering effect on anyone that is placed under your command. I was with the Fleet Marine Force as a Corpsman and it is a big risk letting you supervise men or women. I have had several cases where I had to disqualify men from coming onto active duty until it is reviewed by a psychiatrist who could clear the person in question for active duty or even retention in a reserve component.

Putting false statement on a physical is a punishable offense if they wanted to push it. You should re-evaluate your desire to be in the military and decide if it is really what you want. Getting caught doing something like that on active duty would likely get you a quick trip home and an other than honorable discharge.

I know that a lot of people would say these statements are harsh, but I assure you, they could happen. In any case, I wish you luck in your decision.

At this point, you have little recourse but to let things play out. It is best that it was caught so early, and at this stage, most they are likely to do is to deny you enlistment. As for playing "dumb," I think you've already done this. (Sorry, I am not being mean, but this was not a smart thing to do.) At any rate, if they do allow you in, and note your heart condition, (be sure that they do!) you can then receive treatment by the VA, long after you are out of the military, if such treatment becomes necessary in the future.

Dude! If they let you in. Don't go into military intelligence.

Play it out and find out what the DR'S say. I doubt UCMJ will happen. Don't worry, 'it is what it is'

I don't remember a single Dr's visit I ever had from before I was around 12 or 13.