Assessment of coronary artery disease is a highly relevant problem in current cardiology. Although, coronary angiography still remains the ultimate diagnostic test to prove the presence of coronary narrowings, it is increasingly becoming obvious that a refine understanding of the atherosclerosclerotic lesions and its consequences on perfusion of the underlying myocardium requires much more than just the silhouette of the arterial lumen provided by contrast angiography. This knowledge together with the current therapeutic invasive approaches has led to the introduction of new invasive methods to demonstrate the haemodynamic significance of a given lesion. In this brief review we describe the importance, feasibility and usefulness of transstenotic pressure gradient measurements. Furthermore, we provide the description of myocardial fractional flow reserve as a new functional index for the assessment of the coronary stenosis severity and its effects on maximal myocardial perfusion. This index, by interpreting the transstenotic pressure gradient in combination with mean aortic and central venous pressure offers a complex and easy assessment of coronary haemodynamics. On the basis of our recent experience we discuss the applications of the presented concept in daily clinical practice. (Tab. 3, Fig. 4, Ref. 25.).