I know exactly how you feel. We got our new boxer puppy and at his puppy wellness exam the vet said that he had a grade 3 heart murmur. When then took him for a second opinion to the same Vet who checked out the rest of the litter, it was confirmed that he does have a heart murmur. Two things to ask your vet or check yourself
1. Is the Heart Rate elevated? The heart rate will elevate to compensate for the fact that the heart is not working/pumping as effectively has it should to keep up the demand for oxygen delivery to the rest of the body. Normal heartrate anywhere between 150 to 170 (this is resting) A higher then normal resting heart rate is not a good sign even if the heart murmur was graded at 1 to 2. Double check the literature on the resting heart rate figure I quoted above?
2. How strong is the pulse in the back legs. If the pulse is weak, this is bad because it is telling you the heart is not working well enough to supply good blood flow to the extremities. If the pulse is good and strong, it is telling you despite the problem with the heart (what ever is causing the heart murmur), it is still able to pump the blood.
Maybe you already checked with your vet on these issues?
My thoughts are with your family