An anticoagulant (see ANTICOAGULANTS), usually given by mouth on a daily basis. It is indicated for the PROPHYLAXIS of embolisation (see EMBOLISM) in rheumatic heart disease and atrial fibrillation (see HEART, DISEASES OF); after prosthetic heart-valve insertion; and prophylaxis and treatment of venous thrombosis, PULMONARY EMBOLISM and TRANSIENT ISCHAEMIC ATTACKS (TIA). The initial dose depends upon measuring the INTERNATIONAL NORMALISED RATIO (INR). Warfarin is avoided during pregnancy (especially the first and third trimesters), and in cases of PEPTIC ULCER, severe HYPERTENSION and bacterial ENDOCARDITIS. The most important adverse effect is HAEMORRHAGE (see PANCREAS, DISORDERS OF). (See also COAGULATION.)