Addressing activists at the Tory spring conference in Manchester, the Prime Minister sought to cast the contest as a personal battle with Ed Miliband, accusing the Labour leader of heading a "bunch of hypocritical, holier-than-thou, hopeless, sneering socialists".
He said that a Conservative government would ensure patients across England would be given full access to hospital services seven-days a week by the end of the parliament in 2020.
He coupled his promise of better healthcare with a blistering personal attack on Ed Miliband, warning that the Labour leader was not up to the demands of leading the country.
"Now five years in this job teaches you some things. I know what this role needs - and frankly, I don't think Ed Miliband has it," he said.
"Some might say 'Don't make this personal', but when it comes to who's prime minister, the personal is national.
"The guy who forgot to mention the deficit could be the one in charge of our whole economy.
"The man who is too weak to stand up to the trade unions at home could be the one facing down our enemies abroad.
"The leader who thinks leadership is climbing aboard the latest bandwagon - he could be the one taking the make-or-break calls in the middle of the night."
Mr Cameron said that only he or Mr Miliband could enter No 10 after May 7 - as he accused the Labour leader of planning to "crawl up Downing Street on the coat-tails of the SNP".
He said that under Miliband, Labour was no longer the party of working people, having betrayed its traditional values.
"The truth is that Miliband's Labour Party isn't about liberating working people - it's about telling you what to do," he said.
"The same old condescending, bossy, interfering, we-know-best attitude of the Hampstead socialist down the ages."
On the NHS, he acknowledged that gaining access to healthcare services outside normal working hours was "too hard" but pledged that would change under a Conservative government.
"For years it's been too hard to access the NHS out of hours. But illness doesn't respect working hours. Heart attacks, major accidents, babies - these things don't just come from nine to five," he said.
"And the truth is that you are actually more likely to die if you turn up at the hospital at the weekend. Some of the resources are not up and running. The key decision-makers aren't always there.
"With a future Conservative government, we would have a truly seven day NHS.
"Already millions more people can see a GP seven days a week, but by 2020 I want this for everyone with hospitals properly staffed, especially for urgent and emergency care, so that everyone will have access to the NHS services they need seven days a week by 2020 - the first country in the world to make this happen."
However the plan came under attack from doctors' leaders who accuse the Prime Minister of "shameless political game playing".
Dr Mark Porter, who chairs the British Medical Association council, said the Conservatives had not even committed the funds needed to maintain existing services.
"The £2 billion extra funding that has been pledged falls far short of what is needed to deliver existing services, let alone fund additional care," he said.
"The NHS is recovering from one of the worst winter crises on record, during which some hospitals were forced to close their doors because they couldn't cope.
"With existing services stretched to breaking point, a majority of hospitals facing crippling budget deficits and frontline staff under extreme pressure, the NHS needs far more than just words to deliver extra care.
"Without a detailed, fully-costed plan to provide the staff and resources needed to deliver more seven-day services, this is at best an empty pledge and at worst shameless political game playing with the NHS ahead of the election."