Underworld don Dawood Ibrahim's brother Iqbal Ibrahim Kaskar, who is a prisoner in Thane Central Jail, was referred by the jail authorities to JJ Hospital here, on Monday.
Kaskar complained of chest pain and giddiness.
He was brought to the hospital at 10.15 pm and is currently stable. However, he is being monitored as of now.
On September 18, Thane anti-extortion cell (AEC) arrested Kaskar on the charges of extortion, from his Mumbai residence after a complaint was filed by a builder who was facing extortion threats since 2013.
The builder was taken into confidence and a complaint of extortion was registered at the Kasarvadavali Police Station.