Mtawarira has pulled out of Saturday's match against Ireland in Dublin and will be replaced by CJ van der Linde, the Springboks have announced.
Heinke van der Merwe, who has played in one Test for South Africa in 2007, will take Van der Linde's place on the bench.
A statement on South Africa's official website said: "The decision to withdraw Mtawarira is a precautionary measure after he had a recurrence of mild heart palpitations on Saturday morning.
"Mtawarira has been admitted to hospital for observation on Saturday morning. A decision on his continued participation on the tour will be taken at a later stage."
A further update said the 27-year-old was later discharged from hospital.
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