The need for and the design of invasive procedures in patients with valvular heart disease should be based on the careful evaluation of the patient with history, physical examination, and appropriate noninvasive testing. The number of parameters measured, angiograms performed, and interventions performed during catheterization is determined by the suspected pathology and the clinical status of the patient. The ability to amend the planned sequence and number of measurements as the study progresses must be preserved, so that the most useful data to be used in patient management can be obtained. Knowledge of the limitations as well as the advantages of each technique is necessary to obtain the most accurate data and to interpret the results obtained. It must be recognized that invasive procedures will not always answer all the questions and, in fact, may raise new ones. They are, however, an indispensible part of the evaluation of patients with valvular heart disease, as most surgical and many medical decisions cannot be made without them.