Can Tiny Bubbles Offer an Alternative to Catheters for Assessing Pressures Inside the Heart? Investigating Ultrasound Contrast Agents as Pressure Sensors Against Gold Standard Catheter Pressures in Cardiac Catheterisation Patients.

Inclusion Criteria: * Participant is willing and able to give informed consent to participate in the study * Patients who require a cardiac catheterisation procedure as part of their standard medical care * Good acoustic windows for echocardiography when lying flat on their back Exclusion Criteria: * Known previous allergy to SonoVue, used in ultrasound contrast scans * Known allergy to any of the components of SonoVue microbubbles, for example, sulphur hexafluoride or polyethylene glycol (PEG), also known as macrogol, which is in bowel preparations used during colonoscopy and certain laxatives * A hole in their heart that lets blood flow from the right side to the left, skipping the lungs * Very high blood pressure in the arteries of the lungs (severe pulmonary hypertension) * Uncontrolled high blood pressure (hypertension) * Adult respiratory distress syndrome (ARDS; where severe lung inflammation prevents enough oxygen from reaching the body) * Current use of the medicine dobutamine (used to treat heart failure), or have been advised not to take dobutamine * Moderate to severe heart valve disease that could affect the catheter measurements * Recent acute coronary syndrome or unstable ischaemic cardiac disease, where blood flow to the heart muscle is reduced * Pregnant or may be pregnant * Participation in a clinical trial of a medicine within the past four months, to avoid any possible interactions with SonoVue * Participating in other research that would prolong their cardiac catheterisation procedure, to ensure that the overall process does not become too tiring or burdensome