The goal of this single center prospective controlled observational and interventional trial is to investigate and compare origin of air emboli when different venous cannulation methods is used in patients undergoing cardiac surgery with extracorporeal circulation.

40 consecutive elective patients will be included in two groups, depending on the procedure requiring bicaval or cavoatrial cannulation. After assorted into respective group, patients will be block randomized (five groups consisting of eight patients each) to either intervention group (low venous reservoir volume, 200-300 mL) or control group (venous reservoir volume > 300 mL).

Primary endpoint is to investigate if the amount of air emboli passing through the oxygenator to the arterial line differs between bicaval and cavoatrial venous cannulation during extracorporeal circulation. Secondary endpoints are the relative difference in amount air emboli between the groups, if there is any correlation between the amount of air in venous line and the amount of air passing through the oxygenator to the arterial line during extracorporeal circulation, and if difference is seen on the amount of air passing through the oxygenator depending on the level of volume in the venous reservoir.

Inclusion Criteria:

• Patients > 18 years
• Elective bicaval cannulation (mitral valve repair/replacement (MVR) or MVR + coronary artery bypass grafting (CABG))
• Elective cavoatrial cannulation (aortic valve repair/replacement (AVR) or AVR + CABG
• Planned normothermia (35-37˚C)

Exclusion Criteria:

• Acute heart surgery
• Adult Congenital Heart Disease (ACHD) surgery
• Endocarditis
• Reoperation (primary procedure > 2 years ago)
• Perioperative iatrogenic adverse events (major bleeding, aortic dissection, other severe complications)