Inclusion Criteria:  Male or female patients aged ≥ 18 years old. Signed informed consent by patient or legal representative.  ICU admittance for sepsis defined by the Sepsis-3 criteria as a life-threatening organ dysfunction caused by a dysregulated host response to an infection.  Organ dysfunction is defined by 1 of the following:  a. Increase in SOFA score of ≥2. i. The baseline SOFA score can be assumed to be zero in patients not known to have pre-existing organ dysfunction.  b. Acute kidney injury i. Defined as eGFR < 15 mL/min. c. Acute respiratory distress syndrome i. Defined by the Berlin criteria. d. The need of mechanical ventilation. e. Alteration in mental status.  The patients have to be included in the study within 72 hours of ICU admission due to sepsis. M6229 has to be administered within 84 hours after ICU admission due to sepsis.  Exclusion Criteria:  Subject has an advance directive to withhold life-sustaining treatments. Subject is breastfeeding or intents to get pregnant within 30 days of enrolling into the study.  Subject is of childbearing potential and has a positive pregnancy test.  a. A woman is considered to be of childbearing potential under the age of 60 years, unless surgically sterile.  Confirmed SARS-CoV-2 infection in the 14 days before admission. Clinical suspicion or confirmation of a viral hemorrhagic shock syndrome including, but not limited to, dengue fever.  Bleeding risk:  a. Clinical: i. Active bleeding; ii. Head trauma; iii. Intracranial surgery or stroke in the past 3 months; iv. History of intracerebral arteriovenous malformation, cerebral aneurysm or mass lesions of the central nervous system; v. Cerebral haemorrhage; vi. History of a bleeding diatheses; vii. Gastrointestinal bleeding in the past 6 weeks; viii. Presence of an epidural or spinal catheter; ix. Contraindication for IV therapeutic UFH. b. Laboratory: i. Platelet count <50 x109/L; ii. INR >2.0; iii. Baseline aPTT ≥45 seconds prior to enrolment, 1.5x upper limit of normal (ULN).  Use of any of the following treatments:  UFH to treat a thrombotic event within 12 hours before enrolment; LMWH at a higher dose than recommended for prophylactic use within 12 hours before the infusion; Warfarin (if used within 7 days before study entry AND if the INR exceeds 2.0 at enrolment); Direct oral anticoagulant (DOAC) use 3 days prior to enrollment. Thrombolytic therapy within 3 previous days; Use of IIb/IIIa inhibitors within the previous 7 days. Confirmed antiphospholipid syndrome. Known allergy to fish. Cardiopulmonary resuscitation in the previous 7 days. Liver failure defined as Child-Pugh Score Class C. Abnormal liver function (ASAT and/or ALAT > 5 times upper limit of normal (ULN)). Chronic or acute kidney disease (eGFR<30 mL/min) or dialysis dependent at the moment of study inclusion (including continuous veno-venous hemofiltration (CVVH)). Extracorporeal membrane oxygenation (ECMO) support dependent. Pulmonary embolism or clinical suspicion of deep venous thrombosis (DVT). Life expectancy of less than 24 hours. Treating physician refusal. Known adverse reaction to UFH, including heparin induced thrombocytopenia (HIT). Participation in any other investigational drug study or other interventional study with interfering endpoints. Any other clinical condition which, in the opinion of the investigator, would not allow safe completion of the protocol.