There are common and benign heart rhythm irregularities. Most folks have them occasionally, some folks more often.
If you have one once a day or once per hour, you might have just gotten unlucky that it popped up during the ten seconds of the EKG.
The FAA will at least require a 24-hour diagnostic test where you were a monitor which records your heart rhythm. If your murmur is infrequent and of the right type, they will give you an unrestricted medical. It's possible that you might need beta-blocker meds, but they are approved for flight use, and more than a few older guys use them.
However...usually the AME can issue a medical pending the outcome of the test. Since it is possible that you have a serious condition, do not delay seeing your regular doctor.
You probably want to contact one of the professional aviation medical consultants to help you with this process.