Inclusion Criteria:

- patients receiving maintenance warfarin therapy with a stable therapeutic
international normalized ratio (INR) between 2 and 3 for at least 3 months,

- patients recruited from the anticoagulation clinics at the National University
Hospital and Tan Tock Seng Hospital in Singapore between June 2002 and June 2004 for
a previous genotyping study (C/00/510, NUH; C/00/535, TTSH, PI-Dr Goh Boon Cher).

Exclusion Criteria:

- patients below 21 years old, or

- patients with liver disease, malabsorption or chronic diarrheal diseases, or

- patients taking drugs that may potentially interact with warfarin.

Dietary advice to avoid foods that may interfere with warfarin pharmacokinetics will be
given to patients during warfarin therapy.