Plaid Cymru leader Leanne Wood says a Labour win in next year's Welsh Assembly elections would be bad for democracy.
The Welsh nationalists leader argues that Labour, who have been in power since the Assembly's creation 17 years ago, has constantly failed to deliver on its promises and has run the health service poorly.
Speaking ahead of her party's conference in Aberystwyth, Ms Wood promised a Plaid government in Cardiff Bay would see 1,000 extra doctors and faster cancer diagnosis times.
She said: "I have a specific message to Labour voters - especially those who are concerned with the direction of the health service.
"Our NHS is being failed by Labour.
"We've got fewer doctors than any other country in Britain.
"We've got the longest waiting times for people to be given the all-clear or a diagnosis for cancer.
"The NHS can no longer be trusted in Labour's hands.
"They've had plenty of opportunities to change those things and they have failed to do that.
"Why would people give them another chance to fail again?
"If Labour were to be elected again, what we can expect is a continuation of what we've got now: declining services in the pubic sector and stagnant if not declining economy.
"It's bad for democracy for one party to be in control for 17 years.
"Ahead of the election we will tell people: if you want more of the same ... don't expect different outcomes."
At the last election in 2011, Labour shook off its former coalition partners Plaid and decided to govern alone - despite being one Senedd seat shy of an overall majority.
Since Ms Wood took over the helm, Plaid have yet to make any major gains in either the EU or UK elections.
But the probation officer turned politician will tell her party faithful that Wales needs fresh thinking and a new government.
She said: "Our nation has got all the right ingredients to be a success story and there's nothing that we can't fix in terms of our problems.
"Under Plaid's plans, we want to ring fence health spending so it's a national priority again.
"That will allow us to invest and recruit 1,000 extra doctors, so that services are safe and doctors there when patients when need them."
Other health packages plotted by Plaid included no more care home charges for people diagnosed with dementia and creating specialist cancer diagnostic centres across Wales.
She added: "Labour have become very good at describing the problem in our NHS.
"But people now deserve a party that's ready to face the challenges, provide the solutions and make the birthplace of the NHS a beacon for future health care."
Ms Wood insisted she was not phased by recent polls suggesting a bounce for Welsh Labour since the election of Jeremy Corbyn last month.
"People should not be under any illusion that a change in leadership for Labour in London will make any difference in the way things are run in Wales," she added.
"If we want to improve Wales's situation then we have to do something different.
"If we want to see a government which will constantly battle for Wales's best interests at all times then it's only Plaid Cymru who can deliver that."
Ms Wood acknowledged her party had gained more attention since she appeared in the televised leaders' debates before last year's General Election.
But she said the increased media coverage was not a "magic wand", and that Plaid had more work to do before they could enjoy the kind of electoral success their Celtic cousins in the SNP had.
Ms Wood - who will be standing for election in Rhondda constituency - said she did not think of the May 6 poll as "death or glory" in terms of her leadership.
"I don't look at things in those terms," she said.
"I just put my effort into everything and do the best I can.
"I look forward to what the people of Wales will say next year."
Plaid Cymru's conference is being held at Aberystwyth University Art Centre today and Saturday.