Patients with poor heart function can, in certain situations, have a further weakening of the heart muscle such that it becomes difficult to provide enough blood to the brain and other organs. In these cases, heart function can be supported by the use of medicines or heart pumps. One of the most widely used medicines is Dobutamine, given as an infusion (a drip). Although Dobutamine has been in use for decades and does improve blood flow to the organs, previous studies have not shown any impact on recovery of heart muscle function and survival. Key to unravelling this discrepancy is to understand the precise effects of Dobutamine on the oxygen supply to, and oxygen usage by, the heart muscle. We also aim to find out whether simultaneous infusion of another drug called Nitrite (naturally occurring substance that is found in beetroot for example, much like GTN) can enhance the beneficial effects of Dobutamine on the oxygen supply-demand balance of the heart. In recent years, major advances in technology mean that it is now possible to obtain this information in patients undergoing coronary angiography procedures by making detailed measurements of heart muscle function and blood flow in the heart arteries using a conductance catheter (measures volume and pressure within the main pumping chamber of the heart) and the Combowire (dual pressure and flow sensor tip angioplasty guidewire). The aim of this study is to understand the effect of a brief infusion of Dobutamine and nitrite on heart muscle function, oxygen supply and oxygen usage through this use of this technology, directly following the patients routine coronary angiogram. Patients will have these measurements taken using the technology described above during the infusion of both dobutamine and nitrite, inserted through blood vessels that reach the heart.

Inclusion Criteria:

1. Left Ventricular Ejection Fraction <40%
2. Patients aged >18 years
3. Able to provide written consent

Exclusion Criteria:

1. Known acquired or congenital structural heart disease such as severe valve disease, ventricular/atrial septal defects
2. Haemodynamic Instability
3. Severe disease in major proximal coronary arteries or planned percutaneous coronary intervention during the index procedure

Patients referred for diagnostic coronary angiography following a diagnosis of heart failure, with a left ventricular ejection fraction of less than or equal to 40%.