Prosthetic heart valves have been in use for almost 50 years and warfarin has been available as an oral anticoagulant drug for almost 60 years. One might expect that after 50 years of progress, little controversy would remain about antithrombotic management for patients with prosthetic valves. However, current guidelines on the management of patients with valvular heart disease published by the American College of Cardiology/American Heart Association (ACC/AHA) in 20061 and by the European Society of Cardiology (ESC) in 20072 differ in several fundamental respects in their recommendations for the antithrombotic management of patients with prosthetic valves. The purpose of this review is to discuss these differences and the evidence on which they are based. In the interests of transparency, it should be stated that the author chaired a committee representing three ESC working groups, which published specific recommendations for the management of patients after heart valve surgery in 20053 and was also a member of the ESC task force which created the 2007 guidelines.2

It must be stated at the outset that there are many areas of agreement between the two sets of guidelines. Both guidelines accept the principle of stratification of anticoagulation intensity according to valve position and risk assessment and agree that, in general terms, many patients can be managed with lower intensity levels of anticoagulation than those recommended in the past. Although both guidelines agree that individual patient risk assessment is important, the American guidelines utilise this only to adjust anticoagulation and/or antiplatelet therapy, whereas the European guidelines emphasise the importance of risk factor reduction or treatment as an essential component of overall antithrombotic management (box 1). There are five principal areas of disagreement between the two sets of guidelines:

1. The categorisation of mechanical valves for risk assessment.

2. The antithrombotic management of …