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.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.