30 days is way too early to hear heartbeats. You won't hear heartbeats until the 8th week of pregnancy. You have to listen closely and they won't beat as loud but much faster than the mom's heart beats. This is also the time to get an x-ray done to see how many puppies there are and the size of them.
Also they usually don't start looking pregnant until they are 6 to 7 weeks pregnant, so you still have a little ways to go.
Here is a great site with a ton of information:
Canine Reproduction Video and Book on Breeding and Whelping dogs by Debbie Jensen for dog breeders and Whelping Supplies needed to deliver puppies.