The model by which physicians measure the lack of blood flow in the vessels that supply blood to the heart muscle is called Fractional Flow Reserve (FFR). FFR is the measurement of the pressure across the vessels that supply blood to the heart. These are known as the coronary arteries. This study involves comparing two FFR wires, the St. Jude Medical Pressure Wire (PW) and the ACIST Navvus Microcatheter (MC) to check the accuracy of the devices. FFR allows real-time estimation of the effects of a narrowed vessel, whereas standard angiography can underestimate or overestimate narrowing, because it only visualizes contrast (the different areas of color) inside a vessel.

Fractional flow reserve (FFR) measurement by pressure wire (PW) under hyperemic conditions has become the invasive gold standard for determining the physiologic extent of cardiac ischemia, and which has been validated in several clinical outcomes studies as a way of optimizing case selection for percutaneous coronary intervention (PCI). More recently a microcatheter (MC)-based sensor measurement of fractional flow reserve has been introduced. Small scale in-vivo comparisons have been performed suggesting the utility of this approach to measure FFR,but these data are limited and have not been independently validated. This non-randomized, prospective study is designed to evaluate the accuracy of MC-based FFR measurement to the PW standard in lesions subjected to FFR assessment in routine clinical practice.

Inclusion Criteria:

1. Age ≥ 18 years.
2. Patient provides signed written informed consent before any study-specific procedure.
3. Undergoing coronary angiography, for silent ischemia, stable angina, acute coronary syndrome, or other acceptable indication per the local standard of care.
4. Angiographically significant (>50% visual estimation) stenosis present in at least one native coronary artery.
5. Undergoing FFR assessment for standard clinical or diagnostic indications

Exclusion Criteria:

1. Aorto-ostial lesion location within 3 mm of the aorta junction (both right and left).
2. Vessel(s) and lesion(s) not amenable for PCI, for example diffuse disease.
3. Currently participating in another clinical study that interferes with study results.
4. Pregnant or nursing subjects and those who plan pregnancy in the period up to 1 year following index procedure.
5. Any other medical condition that in the opinion of the investigator will interfere with patient safety or study results.
6. High degree A-V block, sinus node disease.
7. Known hypersensitivity to adenosine