Neozap.com - About ECG s
Put simply, ECGs are Electrocardiograms - recorded using a device that measures the electrical impulses of the heart. Some heart conditions can be partially diagnosed through the ECG, but mainly - they're cool.
A typical trace looks like this:
(Image taken from R. Klabunde's site www.cvphysiology.com)
The P wave is associated with the depolarisation of the atria, the QRS complex is associated with the depolarisation of the ventricles and the T wave is associated with the repolarisation of the ventricles.
These resources have a lot more detail (click to navigate to the page):
Use google to find more about ECG's: