A good general overview of cardiac MRI can be found at www.virtualcardiaccentre.com

The Society of Cardiovascular Magnetic Resonance have an excellent website with excellent content and links to further resources. www.scmr.org

Within the UK there are several high volume cardiac MRI units using a variety of different platforms.  I recommend www.leedscmr.org

Magnetic resonance imaging is, by its very nature, complex. www.reviseMRI.com helps make sense of this technology.