Junior doctors' dispute: What next?
The action came after the British Medical Association (BMA) and the government failed to reach agreement on a proposed new contract for junior doctors.
The BMA, which is concerned about pay for weekend working, career progression and safeguards to protect doctors from being overworked, said the strike had sent a "clear message" to the government.
However, Health Secretary Jeremy Hunt described the walkout as "completely unnecessary" and urged junior doctors to return to the negotiating table.
The last time both sides met formally was on Friday, but negotiations were put on hold while the strike took place.
Officials from Acas said they would hold discussions with both sides on Thursday and Friday, although government sources said they were still prepared to impose the contract if the deadlock could not be broken.
Danny Mortimer, chief executive of NHS Employers, which represents the government in contract talks, said he hoped that would not happen.
"I'm really hopeful that when the BMA return to the talks we can give junior doctors more confidence in both the pay offer that we're putting to them, but also the improved protections we want to put in place around their safety.
"I am desperate to avoid another repeat of industrial action at the end of the month. It's not in their interest and it's not in the interest of patients.
What is the dispute about?
The row between junior doctors and the government is over a new contract
Talks broke down in 2014, but the dispute has escalated since the summer after ministers said they would impose the deal
Ministers offered doctors an 11% rise in basic pay last year, but that was offset by curbs to other elements of the pay package, including payments for unsociable hours - they have maintained there is not extra money for junior doctor pay
The government says the changes are needed to create more seven-days services, but the BMA warns safeguards to keep a lid on excessive hours are being weakened and also has concerns about career progression and weekend pay
A 48-hour strike is scheduled for Tuesday, 26 January - emergency cover will again be provided
An all-out junior doctors' strike is planned for Wednesday 10 February - emergency cover will not be provided
The walkout by junior doctors happened as hospital bosses continue to play catch-up after thousands of operations were cancelled at the start of December - when doctors were first due to go on strike.
That walkout was called off at the last minute to allow talks to restart.
The NHS is meant to ensure patients are seen within 28 days of a cancellation, but that is expected to prove difficult to achieve given the numbers in the system and the fact it is winter - the busiest time for hospitals.
A spokeswoman for NHS England apologised for the disruption caused on Tuesday, saying cancelled tests, appointments and operations would be rescheduled "as soon as is possible".