Assessment of endothelial functions is an important area of medical research. Endothelial functions provide vital information for the management of coronary artery disease (CAD). As a measurable parameter, endothelial functions give a prognostic index that integrates the overall stress imposed by coronary risk factors. Evaluation of endothelial function by non-invasive modes using ultrasound probes is a sensitive and hazard-free technique. However, standardization of the technique is of prime importance to generate a reliable data in the clinical practice.