Topical heparin improves pain in 95.7% of SVT patients — but does NOT replace systemic anticoagulation when clots are high-risk. This 2026 NIH-backed guide covers the anti-inflammatory mechanism, the 2002-patient Thrombophob study, a 7-scenario treatment table, how to distinguish SVT from cellulitis, when fondaparinux for 45 days is required, and DVT and pulmonary embolism warning signs.