To compare two different stress echocardiograms (conventional Stress echocardiograms or Real-time Myocardial Contrast Stress Echocardiograms) that are in routine clinical use. The information, including the digital images that are collected during the stress tests is used to determine if the usse of specialized imaging techniques and ultrasound contrast can better detect blockage in blood flow to the heart and predict how patients outcome may be affected by this detection of a blockage.