Raised international normalised ratio (INR): is it a cause or an effect of late cardiac tamponade?

Two cases of late cardiac tamponade after valve replacement surgery are reported: both patients were treated with oral anticoagulants (warfarin) after operation. An erratic response in the international normalised ratio (INR) was found before the diagnosis of late tamponade. It is suggested that this response of the INR may be an early indicator of late cardiac tamponade rather than a cause.