Recent development in ultrasound technology has made it possible to visualise noninvasively human coronary arteries (including diameter changes) by using transthoracic echocardiography . Moreover, Doppler technology allows measurement of flow velocities in the coronary arteries. This makes it possible to study human coronary reactivity in various provocations. This has earlier been possible only in peripheral arteries like in studies of vascular endothelial function by studying flow mediated dilatation of brachial artery. Computed X-ray tomography of the coronary arteries has been widely taken in clinical use recently. The method yields anatomic images of coronary arteries comparable to invasive coronary angiography, but does not allow evaluation of the pathophysiological consequences of possible flow obstruction due to coronary calcifications. Therefore, it often leads to nuclear studies of myocardial perfusion.