Mugzy is 1.3 years old. Last week, he started 'limping' on his back leg. We brought him into the vet who could not find anything wrong with his leg or a reason for him limping. She gave us some pain medication in case it happened again. While he was there, she said he had developed a grade 3 heart murmur. She told us, nothing to worry about, come back in 6 months and see... Mugzy goes running almost every morning for about 1 - 1/2 hours at the park. The other day, while running with the other dogs, he came back limping. This time, he had 'stubbed' his toe. His 'toenail' looked broken and he was limping bad. Took him back to the vets. This time (a different vet) cleaned it out and bandaged it, but told us that with his heart murmur he shouldn't be running at all. Now we are confused. One tells us, no problem, just watch him, the other says don't let him run at all. After the holidays, we are going to get the test done to detemine what the cause of the murmur is. Our biggest concern is not letting him run in the meantime. He enjoys his run IMMENSLY. After the 'toe' incident, he couldn't go for 2 days to the park and was just misearble. Also, he seemed as if he was 'depressed'. He did go for long walks, but wasn't allowed to run, not the same. Does anyone have any information about a grade 3 heart murmur they can share? Our biggest concern is letting him run and he has a heart attack?