'pends perhaps on how woolie the subject is.

I'm sure you're aware of the need to "smash firmly" against the x-ray film holder for the common annual exams(?) - although I'd hope suspect that shaving isn't required...

Placing EKG pickups would likely have resulted in a request for "spot shaving" in several areas, since it's necessary to get good "adhesion" of the multiple pickups.

Ultrasound generally requires a smooth and even skin contact for good transmission, even though the skin isn't being examined. With "enough grease" a fair amount of hair probably can be accomodated, but most animals would get a better test with some local removal. A doppler-ultrasound would be a likely kind of test, but at least for humans the area examined is likely to include the aorta and adjacent conducting vessels, rather than or in addition to just the heart itself, so the location and direction of exit of the vessels would be as significant a factor in what, and how much, hair needs removal as the simple "where is the heart." The location(s) to be examined might also be affected by the kind and location of any prior problem.

Doing the shaving at home in advance would likely be less stressful for the dog than having it done by "strangers" at the vet; but if some adjustment is required the shaving should be something with which the familiar person could assist, to help calm the pet while any necessary "improvements" are done after arrival.

John