Prosthesis-patient mismatch (PPM) was first proposed by Rahimtoola in 1978 and is defined as an obstruction of the ventricular outflow or inflow tract that occurs when the effective opening area of the prosthetic valve is smaller than that of a normal human valve after implantation in a patient. Because almost all valve replacements are followed by a prosthetic valve with an effective opening area smaller than that of a normal human valve, in fact the definition has now evolved to mean that the effective opening area of the prosthetic valve is too small relative to the patient’s body surface area, resulting in excessive postoperative transvalvular pressure differential. Parameters associated with prosthetic valve-patient mismatch include the geometric orifice area index, the effective orifice area index, and the expected orifice area index. The indexed geometric orifice area (IGOA), which is obtained by dividing the geometric orifice area by the patient’s body surface area as measured in vitro by the manufacturer, is objective, not influenced by the subjectivity of the measuring physician, and easily obtained. However, because valve opening area is influenced by various factors such as the angle of the valve in the body, it does not truly reflect the performance of the valve in the patient’s body, and the results are usually overly optimistic and tend to overestimate the effective opening area. The effective orifice area index (IEOA, the indexed effective orifice area) is obtained by dividing the effective orifice area by the body surface area. The effective orifice area is an in vivo value measured by ultrasound after the procedure, and it is a more realistic reflection of the valve performance in vivo. Sainte-Foy reported that only 21 of the 31 patients measured by the continuous equation method by an internist had results that were accepted by both the internist and the investigator, and the other 10 patients required a repeat ultrasound examination for confirmation. The projected IEOA, the projected indexed effective orifice area, is obtained by dividing the projected orifice area by the body surface area, using the effective orifice area of the valve in question as described in published research articles instead, which is both more readily available and more realistic. reflecting the performance of the valve in vivo, and is now becoming widely accepted. However, it is difficult to predict prosthetic valve-patient mismatch using predicted orifice area because of the influence of outflow tract and aortic root morphology on the angle of the valve at the aortic root and its performance. Each of these three parameters has its own advantages and disadvantages, but there is not yet a parameter that is both simple, fast, and objectively accurate for easy evaluation of prosthetic valve-patient mismatch.