Hi!
I had a complete workup last year, when I was first pregnant. I have MVP (mitral Valve Prolapse, a type of heart murmur), that has never caused a problem, and was fine during pregnancy. I get checked every 5 years just to be sure it is OK.
Anyway, just some reassurance--if they do an echo, it is simple, and doesn't hurt a bit. They do it just like an ultrasound for a baby, Mine took about 20 minutes. You just lay there, and breathe or hold your breath when they tell you to.
I also had a halter moniter for 24 hours, which was some electrodes on my skin and a walkman sized recorder, which clipped on to a belt. This 24 hour recording gave the docrot additional info. Neither of these is painful or scary in any way. I always get nervous when I go to the DR, so thought knowing this in advance might help you a bit.
Actually, come to think of it, when our baby was 4 weeks old, she had a complete workup by a ped. cardiologist too--for what turned out to be a completely harmless murmur that she has already outgrown. SHe slept through the whole thing.
Best of luck to you, and good for you for being so pro-active about your health!