On his second day of freedom after serving 23 years in prison for a murder he did not commit, David Ranta suffered a serious heart attack Friday night, his lawyer said.

Mr. Ranta was taken to a New York hospital — his family did not wish to disclose the name — where doctors discovered that one of his arteries was completely blocked and another was halfway closed. Doctors put in a stent and Mr. Ranta was expected to undergo another procedure, the lawyer, Pierre Sussman, said.

Mr. Ranta, 58, was convicted in 1991 of killing a prominent Hasidic rabbi, Chaskel Werzberger, following the failed robbery of a jewelry courier in Williamsburg, Brooklyn, the year before. He was sentenced to 37 and a half years. He was released last week after prosecutors acknowledged that the evidence against Mr. Ranta had fallen apart over the years.

Mr. Ranta was staying in a city hotel with his family, to give him time away from prying eyes after nearly a quarter-century in prison. Re-entering the outside world from the rule-bound and unforgiving world of a maximum-security prison can be a profoundly disorienting experience, say those who have gone through similar experiences.