ADAMTS13 and aortic valve stenosis: ADAMTS-13 declining post-surgery can account for the acute rise in highest-molecular weight multimers of VWF following AVR. Regression of HMWVWF multimers during the weeks following AVR reflects the resolution of the effects of surgery on ADAMTS-13. The persistent increase in multimers documented six months later indicated the proportion attributable to AS alleviation.