This is a single-blinded, randomised, crossover investigation comparing the investigational device using intra-coronary (IC) Adenosine infusion to the standard intra-venous (IV) infusion method used for obtaining FFR measurements. All subjects requiring on a clinical basis a pressure wire assessment of intermediate coronary artery stenosis(es) will be eligible to take part in the investigation.

Coronary artery disease is the most common type of heart disease that affects millions of people worldwide. It is caused by a narrowing or blocking of the arteries (known as stenosis) due to plaque, which restricts blood flow and reduces the amount of oxygen to the heart.

Over the past decade, fractional flow reserve (FFR) measurement has been increasingly used in cardiac catheterization laboratories, providing a straightforward and readily available quantitative assessment of the functional severity of a coronary artery stenosis, as the ability of the cardiologist to discriminate between stenoses that can cause ischemia and those that are physiologically insignificant on the basis of coronary angiography alone is limited.

Measuring FFR determines the ratio between the maximum achievable blood flow in a diseased or narrowed coronary artery and the maximum blood flow in a normal coronary artery. This ratio represents the potential decrease in coronary flow distal to the coronary stenosis.

FFR is easily measured during routine coronary angiography by using a pressure wire to calculate the ratio between the coronary pressure distal to a stenosis or a diseased segment and the aortic pressure under conditions of maximum myocardial hyperemia. An FFR of 1.0 is widely accepted as normal. An FFR lower than 0.80 is generally considered to be associated with coronary ischemia and widely accepted in favour of revascularization over conservative management.

The current standard methods of measuring FFR is to insert a pressure wire into the coronary artery while the hyperaemic agent, normally adenosine, is delivered by continuous intravenous infusion via a central femoral vein, a large ante-cubital peripheral cannula or intra-coronary bolus injection.

The investigational device in this clinical investigation is an FFR catheter being developed by Diasolve Limited; a UK based medical device development company. The FFR catheter is a combined pressure wire and hyperaemic agent delivery catheter, which allows simultaneous delivery of a pressure wire and administration of the hyperaemic agent directly into the coronary ostium or most proximal section of the coronary artery, when performing a FFR measurement using currently available pressure wire systems such as Pressure Wire Certus or Prestige from St Jude Medical.

Inclusion Criteria:

1. Ability and willingness to give written informed consent prior to investigation participation.
2. Has given consent to undergo hospital's diagnostic or interventional coronary procedure.
3. Male and female subjects aged 18 and over.
4. Ability to communicate well with the investigator and to comply with the requirements of the clinical investigation.

Prior to randomisation:

1. Coronary angiogram demonstrates at least one coronary stenosis of intermediate severity (40-70%), in a non-infarct related artery, which requires FFR measurement for physiological assessment.

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Exclusion Criteria:

1. Known sensitivity to adenosine or any of its excipients
2. Technically inaccessible stenosis(es)
3. Acute ST segment elevation myocardial infarction (STEMI)
4. Haemodynamically unstable
5. Presence of any clinically significant medical condition as determined by the investigator
6. Participation in another clinical investigation within the three months prior.

individual data will not be shared