For the INR, PT and TTR outcomes paired t-test will be used at a two-sided 5% level of significance. These analysis will be per protocol, i.e., data from patients that during the follow-up start treatment with substances or drugs that interact either in a moderate or major way or are contraindicated when used with warfarin (Annex I) will be excluded [update: multiple t-tests would not be adequate because nominal significance levels would not reflect the actual alfa, and thus we decided to apply multilevel mixed-effects linear regression. We have new definitions for per protocol analyses.].