Heart experts have reassured people aspirin is the best drug to prevent heart attacks in high risk individuals, after a patient group raised concerns.
Aspirin helps prevent blood clots forming
The British Cardiac Patients' Association had suggested other, more expensive, heart drugs might save more lives.
It said many people who have had a heart attack or stroke go on to have another event despite aspirin therapy.
But the British Heart Foundation backed current guidance recommending aspirin.
The National Institute for Clinical Excellence says anyone who has previously had a heart attack or stroke, or who have a condition that makes them at high risk of such cardiovascular events, should take drugs to discourage blood clots from forming - aspirin and dipyridamole.
It says the more expensive anti-clotting drug clopidogrel should only be used by those who can't take low-dose aspirin, for example because of potential side effects or dangerous interactions with other medication that they have to take.
But Eve Knight said: "There are two main concerns that we have. Within the guidance, there are many, many people who would go on to have a second event."
People who have had a heart attack or a stroke are at significant great risk of having a second event, particularly within the first six months.
"She said: That's where aspirin or a combination of aspirin will have failed. And there is no clear guidance as to what should happen then.
"The only real mention of clopidogrel is for people who are aspirin intolerant."
She said clopidogrel should be used more frequently.
However, the British Heart Foundation stood by the current NICE guidelines.
Professor Peter Weissberg, Medical Director of the BHF, said: "It is now recognised that people who have cardiovascular disease benefit from taking anti-platelet drugs, which helps stop blood platelets sticking together, and so prevent dangerous blood clots forming.
"Aspirin is an anti-platelet drug and is generally the first-choice therapy for these people.
"More people are living with heart disease than ever before - a total of around 2.7 million people in the UK.
"It is vital that each one of these people is treated appropriately for their particular condition, and there are now alternatives to aspirin that can be used in patients who can't or won't take it. This means that no one with vascular disease should be denied this life-saving treatment.
But he added "Review of the current NICE guidelines may be necessary as more research is done into the risks and benefits of other anti-platelet drugs."