This study will assess the amount of energy that the heart will deliver to the central circulation and the efficiency of that energy transfer, in patients undergoing a coronary artery bypass graft operation. Measurements will be taken just after induction of anaesthesia and repeated just after the end of the operation. The total energy delivered by the heart will be calculated by multiplying a pressure curve from the artery in the hand with the instantaneous ultrasound recorded cardiac output flow curve. The energy responsible for the acceleration of the blood volume, known as oscillatory power will also be calculated. The energy transfer will be calculated using a mathematical model based upon other ultrasound and blood pressure recorded variables. We would like to see if any alteration in energy delivered is in part due to impairment in energy transfer or alteration of fraction of oscillatory power rather than a change in total energy production. We would also like to study if there are changes in the oscillatory power after cardiac bypass surgery. The patients will be sampled sequentially into the study. We are not aware of any such studies undertaken in humans previously.

Inclusion Criteria:

• Elective Coronary Artery Bypass Graft patients
• No contraindications to transoesophageal Echo
• Ejection fraction 40% or over

Exclusion Criteria:

• Lack of consent
• Emergency operation
• Prosthetic aortic valve

The population undergoing elective coronary artery bypass grafting typically have multiple cardiovascular risk factors such as hypertension, hyperlipidaemia, diabetes and smoking.