No, your vet is right. A lot of supplements are scams and some can even cause harm.
My last small breed had a heart murmur since the age of 5, no symptoms , lived till age 16 and died of unrelated causes.
I have had other small breeds that developed murmurs as they got older, no treatment required.
Of course if he begins to have symptoms I would talk to your vet, there are probably prescription meds that would help. And you could even take him to a veterinary cardiologist for further testing and evaluation.
The reverse sneeze thing may be unrelated. Does he hack up white foamy stuff? My old guy did that occasionally, not often.
Ps: The only supplement I give these days is one fish oil capsule with the morning meal.
