Inclusion Criteria:  Diagnosed primary venous disease of the lower limbs in stage C2 - C6 according to the CEAP classification, clinical involvement of the venous system of the lower limbs is verified by duplex ultrasonography Presence of objective and subjective symptoms of the disease (classified according to rVCSS score ≥ 4) At the time of the enrolment, patient is not using nor planning to use compression therapy from his own decision or the decision of the treating physician The patient signed an informed consent for inclusion in the clinical trial and consent to the processing of personal data Patient over 18 years of age Male or female patient of non-childbearing potential, i.e.: post-menopausal (at least 2 years without spontaneous menses) or surgically sterile (bilateral tubal occlusion or hysterectomy or ablation of both ovaries); OR of childbearing potential but with a negative pregnancy test result at Visit 1 AND agrees to use a highly effective method of contraception  Exclusion Criteria:  Use of a drug with venoactive effect in the last month Regular use of compression therapy or use of mechanical devices for reduction of oedema in the last month Heart Failure as per NYHA III and IV, congestive heart failure with peripheral oedemas Chronic kidney disease with GF < 30 ml/min (< 0,5 ml/s) and/or proteinuria > 0,5 g/24 hours, nephrotic syndrome, renal oedemas Advanced liver disease (Child-Pugh B and C or laboratory values of ALT or AST more than 3 times upper limit of normal range) Deep venous thrombosis lower limb thrombosis and / or documented residual venous obstruction or deep venous reflux due to post-thrombotic changes in the deep venous system Superficial venous thrombosis of the lower limbs in the previous 6 months Congenital venous / venolymphatic venous malformation Neuropathy of any aetiology Diabetic foot syndrome Refractory (uncontrollable) arterial hypertension (inability to achieve therapeutically systolic blood pressure ≤ 160 mmHg or diastolic blood pressure ≤ 100 mmHg) Symptomatic ischemic disease of lower limbs Lymphoedema: primary, posttraumatic, postoperative, post-radiation, malignant Manual/instrumental lymphatic drainage in the last 6 months Invasive procedure on the lower limbs in the last 6 months Trauma of the lower extremity that has not fully healed Use of oral/parenteral anticoagulants, dual antiplatelet therapy, diuretics, corticosteroids, oestrogens, or progesterone and its derivates Chronic pain treatment ≥ 14 days Psychopharmaceuticals affecting fluid retention (antipsychotics, combined antidepressants) Pathologic obesity (BMI > 40 kg/m2) The patient is currently enrolled in another interventional or non-interventional study Contraindications to the administration of sulodexide according to IB (haemorrhagic diathesis, hypersensitivity to the drug substance or any of the excipients, heparin, heparinoids or other glycosaminoglycans (GAGs), etc.) Patients with active malignant disease or malignant disease in remission for less than 5 years Pregnancy Breastfeeding  Continuous exclusion criteria:  Clinically significant progression of the investigated condition, which requires urgent or early invasive therapy (as assessed by the investigating physician) Onset of any condition requiring initiation of the not permitted medication/treatment Serious adverse reactions Pregnancy  Compression therapy can be initiated anytime during the trial participation in case that patient experiences worsening of the rVCSS score of at least 4 points compared to baseline AND the treating physician decides to prescribe such regimen. Certified/notified compression stockings of class II (23-32 mmHg) based on circular knit are allowed. Patients initiating compression therapy are not excluded but the stocking need to be taken off a day before the scheduled study visit. The treatment allocation in patients initiating compression therapy remain blinded.  In case compression therapy is initiated during study participation, information about the date of initiation, type and adherence is collected in the following visits.  If sufficient proportion of subjects is switched to compression therapy, compression therapy will be tested as effect modifier across CEAP classes.