Procedures like ECGs arent performed at patient request, they're performed by specialists when a qualified physician determines a need for one and refers you to a specialist.
You can't get yourself an ECG not because they're unavailable, but simply because "Joe Random from city X says you need one" caries as much weight with Heart Specialists as "my cousin Bob says you should give me a new laptop" does with warrantee repairmen.
Like msbarnett says, you can't just roll into a clinic and say "I don't feel well and I'm scared and my cousin who's totally a doctor thinks this is what I should do! Also an MRI please!" Go see a doctor, and let them decide what diagnostic tests are appropriate, and you'll get them done.