One of Tasmania's worst serial sex offenders is arguing he should be released from jail because he is too ill to re-offend.

42 year old Ian Robert Smith says there is no longer a threat of him raping another person because his serious heart condition makes physical exertion difficult.

Smith has to take his bid for release to the Supreme Court because he has been declared a dangerous criminal, due to a long history of sex offending.

In 1989, he was sentenced to 18 months jail for the sustained sexual assault of a 14 year old, but months after his release he raped a seven year old girl.

Prosecutors successfully argued he should be locked up indefinitely in 1995, when he was jailed for raping a 19 year old woman.

Smith has been told that without a heart transplant he could be dead within seven years and says the condition means physical exertion is difficult and he is no longer a threat.

He told court when he raped the seven year old he was acting on an urge that was hard to control and likened it to lighting up when you crave a cigarette.

His psychiatrist agreed it may be possible for Smith to overpower someone weaker, like a child.

The court heard his lawyer wants the dangerous criminal order scrapped now and his client released in six months so he can complete the sex offenders' program.

The matter has been adjourned pending clarification from Risdon Prison about when Smith could take part in the program.

If the court rules Smith is no longer a dangerous criminal and can be released, it has no powers to order ongoing supervision or counselling