Echoes are fun!!!
SO not invasive or painful at all... the kids just watch a DVD while the Echo Tech uses the same kind of ultrasound you got when you were pregnant. Mmmm... I should caveat... at a children's hospital the kid's watch a DVD... if this is at an office, bring a laptop or similar just in case so you can play it for them. Typically takes between 10 & 30 minutes (depending on how still the child is).
My son's murmur is totally benign, but I have many friends whose kids have had heart problems since before birth (surgeries on they day they're born, multiple surgeries throughout their childhood, etc.)... one makes these friends by spending a LOT of time at a Children's Hospital.
The vast majority of murmurs are totally benign. If yours isn't, ask to be transferred to the cardiology dept of a children's hosptial. They do dozens of heart surgeries on KIDS every single day and the hospitals are set up for KIDS (we're not just talking size, but also things like having DVD players in Echo rooms, MRIs, beds in room for parents so you don't ever have to leave them alone (ditto procedure rooms always have a parent area), cool things to play with, staff who are soooooo patient with kids (flashlights and toys in their pockets), numbing pffts that are done before IVs and injections so that they don't hurt, playrooms, visiting people (like Disney Princesses, and local Football teams), and other PARENTS who have sick kids that you can reeeeeally learn from/ lean on. And billing depts are phenom. They don't ask if you can pay, they get your child taken care of and then work out the bill MONTHS later (after you've had time to settle in). I've been in hosptials all over the world (we travelled a lot growing up), the Regional Children's Hospitals are just the best, both from a child's and a parent's perspective. Hands down. ((Key word: Regional. Most cities have a children's hospital... go to whichever hospital they send kids to)).
But remember... most murmurs are benign, totally minor things. It's like having a headache. The VAST majority of the time a headache is just a headache, not a brain tumor. But since I'm sure you're looking up scary stuff online... just thought I'd throw out there how incredibly awesome 'worst case scenario' (surgery) can be.