The study will be spread into two parts. In a first part we will clarify methodological aspects of contrast echocardiography: two different contrast agents and three different contrast imaging methods will be evaluated. One imaging method and one contrast agent will be chosen for the second part. In the second part we will analyze the validity of contrast TEE in the operating room. In addition correlation of changes in myocardial blood flow after coronary artery bypass graft (CABG) surgery and improvement in myocardial perfusion as well as global and regional function in follow-up SPECT (Single Photon Emission Computed Tomography) and transthoracic echocardiography, respectively will be evaluated. By means of these data we possibly will be able to predict success of revascularisation at the end of surgery.