Jagan suffered from an abdominal aneurysm, Thaindian News reported.
Jagan, born Janet Rosalie Rosenberg in Chicago, moved to Guyana with Cheddi Jagan, a Guyanese of Indian descent she met while she was a student nurse at Cook County Hospital and he was studying dentistry at Northwestern.
In Guyana, Jagan worked as a nurse in her husband's dental clinic. The couple also became involved in the labor movement, joining the British Guiana Labor Union.
Jagan founded the Women's Political and Economic Organization in 1946.
The Jagans were co-founders of the socialist People's Progressive Party in 1953. They both won political office, with Jagan eventually becoming the longest-serving member of Parliament, and spent two years under house arrest in the 1950s.
Cheddi Jagan was elected president in 1992. His wife became prime minister and first vice president for several months after his death in 1997, and was then elected president in her own right. She resigned in 1999 because of declining health.