Study to measure the ability of a 'fenestrated' venous line cannula to reduce the negative line pressure seen with kinetic-assist active venous drainage (KAVD) in a standard miniaturised cardiopulmonary bypass circuit and thereby increase the flow characteristics of the bypass pump.

To investigate whether a new venous drainage pipe (cannula) which has three sets of drainage holes (three-stage) compared with the standard two-stage cannula, or a three-stage which also has additional windows (fenestrations), can improve the drainage of blood into the circuit, reducing the negative pressure produced and increase the blood flow delivered to the patient. Patients who consent to participate will be randomly assigned to one of three types of venous cannula:

1. Standard venous cannulation with a two-stage venous cannula
2. The three-stage cannula (91437C, Medtronic)
3. The fenestrated three-stage cannula (MC2X, Medtronic)

Inclusion Criteria:

• All patients over the age of 18 years of age scheduled to undergo isolated Coronary Artery Bypass Grafting (CABG) or isolated Aortic Valve Replacement (AVR), who are able and willing to consent.
• Consultant surgeon willing to operate using either Mini-CPB for CABG or AVR surgery.

Exclusion Criteria:

• Re-operation and emergency surgery
• Patients refusing or unable to provide informed consent

No current plan to share data, but would consider if approached.