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Blackshear JL, Safford RE, Lane GE, Freeman WK, Schaff HV.Blackshear JL, et al. Among authors: freeman wk.J Am Soc Echocardiogr. 1991 Sep-Oct;4(5):485-90. doi: 10.1016/s0894-7317(14)80382-9.J Am Soc Echocardiogr. 1991.PMID: 1742036