Ultrasound evaluation of the heart, or echocardiography, is now the most widely used cardiac imaging procedure. It is well established as a reliable method for evaluating cardiac function and anatomy. Ultrasound image quality, however, is limited by the small differences in density between organ structures in the body. Most tissue interfaces in vivotransmit or scatter ultrasound energy; little energy is reflected back to the transducer causing poor resolution. This situation can be improved by the use of an ultrasound contrast agent, which introduces a highly echo reflective interface in vivo.