The health of imprisoned Venezuelan opposition leader Freddy Guevara could be jeopardized due to cardiac arrythmia, according to his father and a doctor who treated him for coronavirus earlier this year.

Guevara, a close supporter of opposition leader Juan Guaido, who is recognized as the country’s legitimate president by the US and others, was arrested on July 12 and charged with terrorism, treason, and an attack on the constitutional order.

His supporters claim the charges are made up as part of President Nicolas Maduro’s government’s campaign to suppress dissent. The arrest happened as Venezuela’s government and opposition prepare for internationally mediated talks to end a long-running political crisis in the economically impoverished country.

“Inadequate medical treatment while incarcerated puts his life in grave danger,” Guevara’s father, Freddy Guevara, told reporters.

Guevara had suffered multiple episodes of arrythmia, for which he received surgery in 2016, his father added.

Venezuela’s information ministry did not immediately reply to a request for comment on Guevara’s health.

Julio Castro, an infectologist who advises the opposition on health issues and treated Guevara for COVID-19 in June, said he was unaware of what evaluation and treatment Guevara had received, in any, in the month he has been held at the Helicoide detention center in western Caracas, run by the Sebin intelligence policy.

“In a normal situation an evaluation should be immediate,” Castro told reporters alongside Guevara’s father. “It is a very complex condition.”

Guevara’s attorney Omar Mora Tosta said the defense team has not had access to him in the month since his arrest, and that a judge denied the team’s July 27 request for Guevara to be transferred temporarily for a medical consultation.