The investigators propose a single center prospective study that will assess two different strategies for measuring Fractional Flow Reserve (FFR) in patients undergoing clinically-indicated coronary angiography in whom FFR measurement is indicated. FFR will be measured with a non-side hole guide catheter (with the guide catheter both engaged and disengaged from the coronary ostium) and with a side-hole guide catheter (with the guide catheter both engaged and disengaged from the coronary ostium) to determine, whether measurements obtained with an engaged side-hole guide catheter are more accurate as compared with those obtained with the engaged non-side hole catheter.

Inclusion Criteria:

• Undergoing a clinically indicated coronary catheterization
• Need FFR of a coronary artery lesion
• Agree to participate and able to provide informed consent

Exclusion Criteria:

• Significant difficulty advancing the pressure measuring guidewire into the coronary artery
• Severe chronic obstructive pulmonary disease
• Severe ostial disease (>70% diameter stenosis within 5 mm from the coronary artery ostium)