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Schwartz SL, Pandian NG, Hsu TL, Weintraub A, Cao QL.Schwartz SL, et al.J Am Soc Echocardiogr. 1993 Jul-Aug;6(4):345-55. doi: 10.1016/s0894-7317(14)80233-2.J Am Soc Echocardiogr. 1993.PMID: 8217202