Secondary analysis: The proportion of patients in each group with major hemorrhage, thrombosis and a composite of all adverse outcomes (thromboembolism, death and major hemorrhage) will be performed using a Chi square or Fisher's exact technique, as indicated. A regression analysis will be performed to determine if baseline variables including the receipt of drug or placebo, demographic characteristics, degree of prolongation of the international normalized ratio or other baseline variables predict adverse events. Finally, the mean INR values in the two groups will be compared using ANOVA.