Professor Sir Stephen Powis said ambulance strikes will create a “very difficult day” for the health service, but suggested heart attacks, and strokes would be covered.
He told BBC Radio 4’s Today programme: “Today is obviously going to be a very difficult day with the health service.
“But we’ve been working very closely with the unions to ensure that emergency services for life-threatening conditions are maintained, and that will include stroke and heart attacks.
“There are increased clinicians in call centres to ensure that the right response goes out to the right incident.”
Ambulance responses are split into categories, with category 1 being the most life-threatening such as cardiac arrest, while category 2 covers conditions such as stroke, heart attack, and sepsis.
Sir Stephen said strokes fall into the higher end of category 2 cases, and clinicians will determine what response is needed.
He advised people to dial 999 “as usual” if they have a life-threatening condition.