Christy Dignam told Ryan Tubridy about his rare health condition on tonight's Late Late Show.
The Aslan singer said: "The thing I've got is called Amyloidosis. There's no cure for it. I think there's only 4 or 5 people in the country that have it. With me, it produces too much protein, the protein affects my heart and my kidneys. So my heart's working at about two thirds of its normal capacity.
"They can hold it at bay with chemotherapy. You usually get a four year hiatus when you finish the chemo, so I finished it two years ago, so I've got two years left before I should come back."
The singer also spoke about a new treatment for the disease which is expected to be introduced in Ireland in a year's time which will will be more targeted than chemotherapy.
Dignam said he was "concentrating on getting better" for the past while and eased things off with Aslan, but promised to "kick back off" again with the band towards Christmas.
He added that since battling the illness and coming to terms with his mortality, he has come to realise that life is all about family and "keeping that unit happy, trying to make them as happy and productive as possible".
The band performed a rousing rendition of their classic track This Is with a choir on the show - check it out below.