(CNN) -- Laura Pollan, a founder of one of Cuba's leading dissident groups, died Friday, her daughter said.
Pollan suffered a heart attack and died at Calixto Garcia Hospital in Havana, Laura Maria Pollan told CNN en Espanol.
The founder of Cuba's Ladies in White had been hospitalized several days ago because of a respiratory complication.
Yoani Sanchez, a Cuban blogger, told CNN that some of Pollan's relatives, friends and fellow dissidents had gathered outside of the hospital.
The Ladies in White, an opposition group, formed after the Cuban government cracked down on dissidents in 2003.
Among the activists arrested then was Hector Maseda Gutierrez, Pollan's husband. He was freed in February.
Members of the Ladies in White dress in white, carry flowers and march to demand the release of political prisoners -- many of whom are relatives and friends of the women.
CNN's Carloo Perez contributed to this report.