The Irish Heart Foundation (IHF) described the results of the study as alarming and insisted more lives could be saved if people reacted faster.
Head of advocacy at the charity Chris Macey said while more people now recognise the signs of a stroke, not enough take the right action.
"These statistics are alarming because there's little point in people knowing when they're having a stroke if they don't know that the only reaction is to call an ambulance immediately," Mr Macey said.
"The average stroke destroys two million brain cells every minute, which means the quicker you get emergency treatment literally the more of your brain can be saved."
He said getting to hospital quickly has a "profound impact" on the outcome of a stroke.
"For those who delay it can mean the difference between walking out of hospital on your own steam within days of a stroke and spending the rest of your life in institutional care, or even death," he said.
As the IHF Fast Awareness Week begins on Monday, figures for the charity from Behaviour and Attitudes showed that only 52% of people would call an ambulance immediately after witnessing or experiencing a stroke.
Some 23% of respondents said their immediate reaction to a stroke would be to tell a family member, friend or neighbour and 12% said they would call their GP.
The IHF said while public awareness of stroke warning signs had increased by 190% since it launched its 'Act Fast' campaign three years ago, it was concerned such a low proportion would call an ambulance immediately.
According to the charity, stroke-related hospital admissions soared by 87% following the campaign launch in 2010 because people knew to go to hospital as soon as they recognised stroke symptoms.
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Results of stroke survey ‘alarming’