Parties should not use the NHS as "a political weapon" in the election campaign, health service bosses say.
NHS Providers chief Chris Hopson said "over-dramatising NHS difficulties" or making "disingenuous" funding claims did the service "no favours".
Both the Tories and Labour are vowing to spend billions to improve care.
But Mr Hopson, who acts for health trust leaders in England, urged parties not to make "empty promises" or create "unrealistic expectations".
The long-term future of the NHS and social care is likely to be a key battleground in the run-up to the 12 December election.
The Tories are expected to trumpet extra spending on the health service in England, including a £2.7bn investment for six hospitals over five years and £100m for a further 34 hospitals to start developing future projects.
This is on top of an extra £20bn in funding agreed by Theresa May's government up to 2023.
Labour argues the NHS is reeling from the tightest funding squeeze in modern history since 2010, which it says has left nearly four and half million people waiting for treatment and seen thousands of cancelled operations last year.
Jeremy Corbyn has said he will end austerity in the NHS via a "proper funding settlement", with the exact details to be announced ahead of the launch of the party's manifesto.
Mr Hopson called for a "proper, mature, evidence-based" debate on what the NHS needs.
"Let's not resort to the cheap political slogans and skimming across the top which is what we've seen over the last four or five elections," he told the BBC's Today programme.
Writing on the Times website, he said it was understandable that during election campaigns politicians should "cast themselves as champions and defenders of the NHS".
However, he warned "it becomes counter-productive when the NHS is used as a political weapon" - something he said leaders in the health service were worried was already starting to happen in this campaign.
It is unrealistic to expect the parties to dial down their highly-charged debates on the subject.
But NHS Providers argues that already things are getting out of hand with signs that the NHS is being "weaponised".
Underlying all this is a warning that the NHS in England cannot seem to keep up with growing demand for care, which is "particularly worrying" with winter looming.
Hospital chiefs are known to be concerned that there was intense pressure in recent weeks before winter had really set in. How that pressure develops before polling day could be a major issue in this campaign.
While there were areas where "the NHS is falling short", he said "over-dramatising or distorting the difficulties for political ends will do nothing to help those frontline staff who are working flat out for patients".
And Carrie MacEwen, from the Academy of Medical Royal Colleges, said undeliverable promises "simply set up the NHS to fail".
"The NHS's role is to manage the health of the nation, not to be used as a tool to swing voters in a three-way marginal," she told the Times. "Our fear is in these febrile times we will see irrational, undeliverable promises or even outright lies."
Labour's shadow chancellor John McDonnell said he agreed that the NHS "shouldn't be weaponised" during the election campaign but voters deserved an "honest debate about it."
Speaking after a visit to Unison headquarters to meet NHS staff, he also repeated that under a Labour government, the health service would be "brought back in house" when privatised contracts "come to an end".
The Tories have repudiated Labour claims that privatisation has exploded in recent years, pointing to figures showing the total number of private contracts has remained static at 7% in the past four years.
Health Secretary Matt Hancock accused Labour of peddling "scare stories" to try and win votes because they have "nothing positive to offer".
"These stories worry some of the most vulnerable people in the country, who the Labour Party used to say they represented," he said in a video message on Twitter. "It is only with the Conservatives, with our strong support for the economy, that we can make sure the health service is always there for you and your family."
But former Conservative health secretary Stephen Dorrell, who is standing as a Lib Dem candidate in the election, said both the main parties were driven by ideology when it came to the issue.
The NHS, he told the BBC Radio 4's World at One, was a "perfect example of a place where our economy works best when the public and private work together".
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