It's an ultrasound, the machine used is often the same model as for pregnancy but with different software and different transducers.
Ultrasound does not penetrate bone or air so unlike pregnancy where you have a small to large target with not much in the way you have a target about the size of a fist hidden behind lungs and ribs.
The same gel is used as for i pregnancy so don't wear your best silk shirt.
You may or may not have electrodes on your chest, it depends on the person doing the test and what they are looking for.
You will probably start off on your side with your hand over your head, the transducer (the bit the tech holds) will be pressed against the gap between your third and fourth rib. It might be a little painful because the transducer needs to be in contact with flesh but also needs to be aimed around lung and ribs.
There will be more recordings made from what will feel like under your left boob, this is to get a different angle.
You may then be asked to lie flat and have recordings made from under your rib cage with the transducer pointing at your neck and also from your throat - this is the one most people feel uncomfortable with but it is quick.
Measurements will be made, probably while you are there, but may be doe after.
The tech, actually they are now called physiologists, will measure the size and function of both ventricles and the valves.
For patients it is mainly boring and at time uncomfortable as you have to be positioned where you can't see the screen.
This is the one test it is easier if you have a light amount of padding.
An echo is more sophisticated than an ECG as it draws a picture of how the heart is working rather than giving a readout. I found it fascinating to see my heart working on the screen...
It's a totally different test measuring totally different things, the ECG records the electrical activity of the heart, that can indicate some structures. An echo actually measures things like the thickness of the ventricle wall, or the shape of a valve.
Guess what I used to do for a living?