An EKG, an echo and a stress test will rule out most of the heart muscle diseases if normal. There are a lot of heart muscle diseases where most of them are ruled out after a normal echo (ultrasound of the heart).
ARVD (as mentioned by itdood) is a special form of cardiomyopathy (heart muscle disease). It is diagnosed after special criteria which include a lot of testing and history. A normal echo and a normal EKG will rule the condition out by a fairly high certainty (and keep in mind, this is a RARE disorder) but if your doctor suspects it, MRI or biopsy are better tests, as itdood said.
echo as mentioned can measure thickness and movement issues. MRI is better and the standard for testing ARVD. Biopsy is also an option for ARVD.
I would think an echo would give a visual on how the heart is expanding and contracting. If there are other tests I am sure someone will chime in.