You may want to check with basic internal medicine clinics/offices, as well as cardiologists. An internal med doc should be able to order the testing, as it can be a pre-requisite before referral to a cardiologist.
fwiw, you may be a little confused as this is a board for feline diabetes. you have one other post on here, also pertaining to human health, so wanted to make sure you are aware you are on a feline health board