Hi!
What an adorable name. Can't wait to see pictures. My only advice would be to get him to your own vet, not the Humane Societies vet, have him checked over and get him started on heartworm medicine. And don't be afraid to change vets if you aren't clicking with the first one. Vets are just like our doctors, some we feel good with some we don't. We have several YT members in CA, perhaps one of them can recommend a vet for you to try.