The convicted drug dealer, John Gilligan, has been admitted to hospital in Portlaoise.
The 50-year-old called prison officers into his cell in Portlaoise prison this morning and asked for medical treatment.
A doctor who examined Gilligan - who is serving 28 years - recommended he be transferred to hospital.
Gilligan was taken under armed escort to the Midlands Regional Hospital where there is a special security ward where inmates from the maximum security prison are treated.
It is understood he is suffering from heart-related problems.
Last October Gilligan was admitted to the same hospital complaining of pains in his arm but was transferred for further tests and treatment to St James' Hospital in Dublin the following day.
