Mauritania's former president; Mohamed Ould Abdel Aziz, underwent what was described as a successful heart surgery on Saturday evening.
Abdel Aziz has been in custody since June facing alegations of corruption.
The former president was admitted to a military hospital on Wednesday for urgent care.
In a statement issued on Wednesday evening, his family said they "feared his physical liquidation" by the regime.
In early November, the Nouakchott Court of Appeal once again rejected a request for the provisional release of the former president.
Last March, Abdel Aziz was accused of corruption, money laundering, illicit enrichment, squandering public property, granting undue advantages and obstructing the course of justice.
The former president has always refused to talk to the investigating judge as he claims to be protected by constitutional immunity.
Abdel Aziz was president of Mauritania between 2008 and 2019.