@starrynight - I've actually had a sonogram before, though not of my heart. I didn't know they could use sonography to do cardiac imaging too! Neat.
Some of those invasive cardiac imaging techniques sound pretty scary. I think if I need a transesophageal echocardiogram I would definitely opt for sedation.
However, the other cardiac imaging types sound like they wouldn't be too uncomfortable. I'm hoping if I ever need to get anything like this done I can just get a CT scan or something.