Although the terms ventricularization and damping are commonly used in the cath lab and are widely recognized as indicating possible flow limitation due to catheter position, their hemodynamic origins and mechanism have not been well studied. Often, they are thought to be synonymous terms. Both patterns are due to distortion of the normal harmonic frequencies of wave conduction. Pressure damping is seen when the outer diameter of the catheter is larger than the ostial diameter or when the tip of the catheter is pressed against the vessel wall. It is characterized by an abrupt decline of mean coronary pressure with narrow pulse pressure and delayed upstroke and downstroke. Conversely, ventricularization is seen when the catheter tip is advanced into an ostial stenosis, partially obstructing flow, and is characterized by a steep decline of pressure in diastole with large pulse pressure, absence of the dicrotic notch, and appearance of presystolic positive deflection. A ventricularized pressure waveform can be considered a hybrid between coronary arterial pressure and coronary wedge pressure.