This is an open-label, prospective crossover randomized controlled trial to investigate wether TACO is solely hydrostatic pressure overload or arises from a combination of hydrostatic pressure overload and capillary leakage, by investigating the difference in change in static pressure parameters (PCWP), dynamic volume parameters (PICCO) as indirect measurements of volume status and capillary leakage after autologous transfusion or saline infusion. The investigators will estimate effective circulating volume following autologous transfusion or saline infusion. Furthermore, the investigators will investigate the effect of fluid loading on the microcirculation.

Coronary arterial bypass grafting surgery patients with reduced left ventricular function will be allocated to either infusion of 300mL saline with a subsequent autologous RBC (cell saver) transfusion of 300 mL at a rate of 10mL/min, or the same in the reversed order. Prior to start of the intervention, 15 minutes following start of infusion and a the end of infusion, the investigators will measure right-ventricular pressure and wedge pressure (PCWP), as well as extravascular lung water index (EVLWI) and CO estimation through PICCO® and Pulmonary Artery Catheter. The investigators will identify fluid responsiveness by performing a passive leg raise test (PLR). The investigators aim to measure total vessel density (TVD), perfused vessel density (PVD), proportion of perfused vessels (PPV), microvascular flow index (MFI), and blood vessel diameters (Øbv) from the oral microcirculation by CytoCam microscope system. The investigators will estimate the effective circulating blood and plasma volume through dilutional infusion of indocyanine green prior to initial infusion, between and at the end of subsequent infusion.

Inclusion Criteria:

1. Age >18 years
2. Elective (non-redo) coronary arterial bypass grafting surgery
3. Reduced left ventricular ejection fraction (<55%)
4. Transfusion of autologous blood (cell saver blood, 300ml, HCT60%, 30min)
5. Informed consent

Exclusion Criteria:

1. Patients with no indication for autologous RBC transfusion
2. Patients with pulmonary hypertension, congenital heart disease, mitral or tricuspid valve disease.
3. Contraindications for PAC placement; coagulopathy, bundle branch block, defibrillator or pacemaker (risk of displacement). External pacemaker placed during surgery is no exclusion criterium.
4. Patients for acute, non-elective surgery
5. Chronic kidney disease stage 4 or higher (eGFR < 30)
6. Massive transfusion
7. Previous randomization in the current trial
8. Postoperative ongoing bleeding
9. Bypass duration > 2 hours
10. Infusion of high dose corticosteroids
11. Hemodynamic instability with a mean arterial pressure (MAP) < 60 mmHg, central venous pressure > 20 mmHg or dependence on high dosages of inotropic drugs after admittance to the ICU
12. Severe arrhythmias
13. Development of severe pulmonary edema during infusion of autologous blood or saline.
14. Elevated liver enzymes
15. Iodine allergy

Masking of investigator is not possible due to nature of intervention.