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Willens HJ, Gómez-Marín O, Heldman A, Chakko S, Postel C, Hasan T, Mohammed F.Willens HJ, et al.J Am Soc Echocardiogr. 2009 Jul;22(7):793-9. doi: 10.1016/j.echo.2009.04.018. Epub 2009 Jun 7.J Am Soc Echocardiogr. 2009.PMID: 19505793