Deaths caused by pulmonary thromboembolism (PTE) are often of forensic interest, due to the frequent preexistence of a traumatic event the suddeness of death, and possible professional responsibility. Early diagnosis of vein thromboembolism is often difficult. Fatal PTE usually presents itself on an unexpected and large scale, chronologically occurring shortly before death and thus irreconcilable with any consequent efficacious therapy. Pharmacological prophylaxis, aiming at reducing the state of blood hypercoagulability, is the elective therapeutic strategy for vein thromboembolism. These are the premises for this work which, after a brief pharmacological and clinical description of heparin prophylaxis and a review of data emerging from a sample of 24 deaths due to PTE, makes some considerations regarding professional responsibility.