Laura Pollan, who helped found the dissident group Ladies in White in Cuba after her husband was jailed in a 2003 crackdown on government opponents, has died in a Havana hospital on Friday at the age of 63, her family and fellow dissidents said.

Pollan was one of Cuba’s leading opposition voices and deeply involved in promoting change on the Communist island until she developed a pulmonary illness and went into the hospital on October 7th.

She had been on a respirator in the intensive care ward of Calixto Garcia hospital ever since and died of cardiac arrest on Friday, said Berta Soler, her longtime co-leader of the Ladies in White.

Husband Hector Maseda told Reuters at the hospital that a medical team had tried for an hour to revive her without success.

“I asked to see her and went to see her body. I was there with her for a while, alone,” said the visibly shaken Maseda.

Elizardo Sanchez, head of the independent Cuban Commission of Human Rights, said the loss of Pollan was a big one for opponents of the Cuban government.“It’s really bad news for the human rights and pro-democracy movement. It’s an irreparable loss. We’ll see with time if others step forward to take her place,” he said.