An echocardiogram is a sonography of the heart. Also known as a cardiac ultrasound, it uses standard ultrasound techniques to image two-dimensional slices of the heart. The latest ultrasound systems now employ 3D real-time imaging. In addition to creating two-dimensional pictures of the cardiovascular system, an echocardiogram can also produce accurate assessment of the velocity of blood and cardiac tissue at any arbitrary point using pulsed or continuous wave doppler...
Check out the website for your school's medical library, or talk to your librarian. I know my school (University of New Mexico) has subscriptions to several different journal databanks...