Election 2015: NHS cash guarantees new Lib Dem 'red line'
Nick Clegg has said the Lib Dems will not sign up to another coalition with any party that does not guarantee £8bn in extra annual funding for the NHS
The Lib Dem leader has been setting out his negotiating position in the belief no-one will win an outright victory.
Other "deal breakers" he has identified include education funding and action on the deficit and tax allowances
Polls suggest the Lib Dems are expected to see a drop in votes and seats but could still hold the balance of power.
In the event of another inconclusive election result, Mr Clegg has suggested that either his party, the SNP or UKIP could play a decisive role and that his party is right to set out its priorities for post-election negotiations in the spirit of accountability.
For his part, David Cameron has set out one "red line", saying he would not serve as prime minister in any government which could not deliver a referendum on the EU in 2017 - a referendum the Lib Dems oppose.
NHS England has said it will require £8bn in extra funding a year by 2020, on top of the above-inflation increases already promised, to ensure it can modernise and meet the growing demands on it from an ageing society.
The Conservatives and Lib Dems have said they will fund this in full. The two parties agreed to a £2bn annual "down payment" last year towards the full amount but have accused each other of a lack of clarity about where the rest will come from.
The Lib Dems have said they will raise an extra £1bn a year, covering the period from 2016 to 2018, through increases in capital gains tax and other tax measures.
After 2018, by which point the party hopes to have paid off the current deficit, they say they will ensure annual NHS budgets rise at least in line with economic growth to meet the remaining shortfall.
Labour has said it will make available an extra £2.5bn this year but will not commit to specific sums after that until it can show how they will be paid for, while UKIP has called for an extra £3bn a year to be pumped into the health service.
Speaking in Manchester, Mr Clegg threw down the gauntlet to his Labour counterpart to go further.
"I have a message for Ed Miliband. You might say you love the NHS - the NHS doesn't need warm words, it needs hard cash.
"So Ed Miliband, put your money where your heart is. That is what the Liberal Democrats will do.
"We know how much money the NHS needs. And we have got a plan, a fair plan, including the wealthiest in society making an additional contribution through the tax system, to make sure our NHS is properly funded.
"I cannot be clearer: this is a red line issue for the Liberal Democrats.
"The Liberal Democrats will not under any circumstances enter into a new coalition government unless we know exactly how the NHS is going to get the money it needs and how it is going to get that money fairly."
Mr Clegg said he would announce "one or two more" red lines over the weekend. Asked if this would include anything on Europe, Mr Clegg said: "Let's just wait and see what I say over the weekend."