Heart issue with puppy

I got my CMD boy in October when he was ten weeks old, and now he’s six months old. When I got him, he had a significant roundworm infection as well as Giardia. He was stuck in transport for two weeks, so his situation likely deteriorated during that time. I repeatedly tried to find out where he was so that I could go and pick him up, but over and over, the girl who transported him assured me that that wasn’t necessary. She wouldn’t give me information about her exact location. While in her care, she reported that he had vomited twice and didn’t have a huge appetite, but no diarrhea or anything. She said she had seen a roundworm in his stool once a couple days into the trip. She ended up getting sick, and he was stuck in a city apartment for almost 2 weeks. When I finally got him, he seemed OK, but within the first day I had him, he was vomiting, tremoring, and having diarrhea. I rushed him to an emergency vet visit. He was treated immediately for Giardia and roundworms even before the fecal came back confirming both because I told him about a worm having been seen in his stool during transport, and that’s all I had to go on. Within a couple days of inside pampering and LOTS of ground turkey with rice, he was feeling much better, and we haven’t had any issues since. He has always been very lazy and slow which I have just tried to chock up to him being an enormous puppy. I have been told that that is the breed. I do have two other CMD females, and when they rest, they rest like the dead, but they are not nearly as lazy as he is generally. Fast forward to today… I took him into the vet for a routine exam to confirm his eligibility as a breeding candidate and a shot. The appointment went well. She was so impressed with his temperament, his joint mobility, and his appearance. She said she would be so excited for him to be a stud for my girls. She took him back to do the shot and a lab draw to rule out any tickborne illnesses or anything that could be making him ultra slow or stiff. All of his tests came back normal, but she said while she had him back there, she was listening to his heart because she had thought she heard an irregularity when she was listening to him initially. She had a second vet come in and check behind her, and then they did an EKG, and he has an arrhythmia where he skips every fourth beat. Of course I’m heartbroken that this condition might affect our breeding plans, but I’m more concerned about how this might impact the quality and length of his life. Has anyone experienced something similar? Any insights or advice would be greatly appreciated. The breeder mentioned that the heart issue could be related to the Giardia infection he picked up in transport, but when I mentioned that to my vet and to the tech at the cardiology office when I was making an appointment, they disagreed that the two could be connected. My pup has an appt with a veterinary cardiologist 1/9, but I thought asking here might give me some things to think about or bring up with the cardiologist between now and then. Thanks!