After a short introduction and overview of normal anatomy, physiology, and pathology of the cardiovascular system, non-invasive and invasive methods in the diagnosis and treatment of cardiovascular disease will be discussed. An important issue is to gain insight in how to adapt and simplify scientific measuring methods to be applicable in clinical practice, without loosing scientific correctness. Adaptation of the heart to valvular disease will be discussed as an example how clinical syndroms develop and to demonstrate the rationale of a scientific approach as the basis for treatment. Principles and techniques as used in right and left heart catheterization will be overviewed, such as pressure measurement in the circulation, flow and shunt calculations, oxymetry, estimation of cardiac output and valve surfaces, etc. Special attention will be paid to regulatory mechanisms in the coronary circulation in health and disease. Finally, monitoring methods of critically ill patients will be dealt with, focussing on the syndrome of shock.