I'm going to guess this is not her first visit with the vet and they haven't said they heard a Heart Murmur before this visit. You have also said she has had a cold. Did they tell you they want you to bring her back in for a recheck on the Murmur in a few weeks or months? If not you need to call them and ask them about doing this. The Murmur could be illness related or even stress related.
We have to take Sassy back in for a recheck since our vet heard a Murmur on her the last visit. If she hears it this time she will send Sassy to the heart specialist to have them run some test on her to see how bad it is. The heart specialist will then tell us what the options are and what we need to do for her.
I will tell you that this is our first time having a vet tell us they heard a Murmur in one of our pets. I can tell you that our YDD has a heart Murmur but it only shows up when she is sick. My Dr told me that this is illness related and only shows up when she is sick.
Our Vet said the same thing can happen with pets so not to get to worried right now. We just have to wait until we go for the recheck and see if they hear it again. Ii do know that I'm a bit concerned as Sassy is very small she is a little cat. Of her litter of 6 only2 kittens lived. The kittens had fleas bad, and were sick when they were little. When you see Sassy with our other cats she doesn't look the same, build is not normal and she walks funny. We are taking her soon as the new kittens need their second set of shots soon.
I will post any information my vet gives me if they hear it again. I would talk with your Vet and ask about the recheck and ask them for information. They should have given you a print out of information and a referral to a vet heart specialist for more testing and followup care. If they blow you off start looking for a different vet and a vet heart specialist. If you can't find this in your area you might want to find the closest veterinary school of medicine. Call them tell them what you have been told and see what they have to say.