Roscommon Fine Gael TD Denis Naughten has voted against the Government on a motion to downgrade Roscommon County Hospital, but colleague Frank Feighan voted for the motion.
The motion by Sinn Féin to retain emergency services at smaller hospitals was eventually defeated 96 to 47.
Mr Naughten said afterwards he had no choice but to vote against the Government, because of promises he made during the election campaign to keep Roscommon Hospital Emergency Department open.
The emergency department at the hospital is to close from next Monday.
Mr Naughten now looks certain to lose his position as Chair of the Dáil Health Committee.
He said voting against the Government was the most difficult decision he had ever taken, but he felt he had no choice as he had given his word to his constituents.
Asked about the party's deputy leader, James Reilly, who had made the original promise to keep Roscommon Emergency Department open, Mr Naughten said he believed Mr Reilly made the commitment in good faith, but it has not been possible to implement it.
He added that he would support the government in making difficult decisions that were in the best interests of the country.
He declined to comment on his position as Chairman of the Dáil Health Committee.
Mr Naughten’s constituency colleague Frank Feighan on the other hand, told the Dáil that he would not be keeping to his election promise to stand by Roscommon County Hospital.
He said events such as the HIQA report and the shortage of junior doctors had overtaken his commitment.
Independent TD Luke 'Ming' Flanagan had encouraged Fine Gael TDs from Roscommon to vote with the Opposition or else 'be classified as traitors til kingdom come'.
In an emotional contribution to the debate, Mr Flanagan said he was in no doubt that lives would be lost if the emergency department closed down.
He pointed out that Ireland's EU-IMF partners would make €9bn from the Irish bailout and that the hospital required just 0.5% of that.
Protest over Roscommon downgrade
A demonstration took place outside Leinster House this evening in protest at the decision to close the emergency department.
Up to 1,000 people have travelled from Roscommon took part.
The protesters held banners and signs calling on Health Minister James O'Reilly to honour his pre-election promise.
There were angry scenes when Mr Feighan came out to address the crowd.
Due to the anger of the protesters, he did not get the chance to speak and he was ushered back into the Dáil.
Earlier in the Dáil, Taoiseach Enda Kenny defended the Government's handling of the health service, and dismissed criticism by the Opposition as 'pathetic'.
Fianna Fáil leader Michéal Martin pointed out that during the election campaign, Fine Gael had promised to retain the emergency department at the hospital.
Sinn Féin's Gerry Adams said citizens had a right to a first class health service.
Mr Kenny said patients at Roscommon would still have access to the majority of treatments they always had, and that the 'leviathan structure' of the HSE had to be reformed, not just in Roscommon but throughout the State.