Iranian opposition figure Mehdi Karrubi has been hospitalized due to a heart condition, his son said.
Karrubi, a former parliament speaker who has been under house arrest since 2011 without being charged, was also briefly hospitalized in March.
Karrubi’s son, Mohammad Taghi Karrubi, told RFE/RL's Radio Farda on July 24 that his father’s health problems have been caused by his detention.
Karrubi has been accused by authorities of insulting Islamic and revolutionary principles.
Karrubi, along with opposition leader Mir Hossein Musavi and his wife, Zahra Rahnavard, were put under house arrest in February 2011 for challenging the establishment over the disputed 2009 presidential vote and also for highlighting human rights abuses.
Rights groups have repeatedly called for the release of the three opposition figures.
President Hassan Rohani has promised to free political prisoners, but he has largely failed to fulfill the pledge he first made during the presidential election in 2013.