New health data from Heart Foundation shows seven in 10 Australians yet to reach their 50s have 'older' hearts.

It comes as the foundation's online heart age calculator, has been used by everyday Aussies curious to know how their ticker is travelling. The calculator compares and individual's heart age to biological age, to better understand the risk of having a heart attack or stroke.

Heart disease is the nation's single biggest killer, claiming 45 lives each day.

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People in their 30s and 40s are of greatest concern according to those who have taken the online test.

Analysis of a sample of more than 71,000 heart age test results for Australians aged 35-49 showed one in eight in this group had a heart age at least six years above their actual age.

Nearly 60 per cent did not know their blood pressure levels, and more than four in five (82 per cent) did not know their cholesterol readings. This equates to about 2.9 million Australians in this age group not knowing their blood pressure and four million not knowing their cholesterol level.

Of those who knew their numbers, one in four had high blood pressure and two in five had a high total cholesterol level.

Heart Foundation General Manager of Heart Health, Bill Stavreski, said the startling results showed why heart disease needed to be on the radar.

"Many younger Australians who took the test have risk factors for developing heart disease down the track. What's just as worrying, is most don't know their blood pressure or cholesterol numbers," Mr Stavreski said.

"This complacency can be a killer because high blood pressure and cholesterol are the two leading risk factors for heart disease and stroke. These conditions often have no obvious symptoms.

"Taking care of your heart and managing your blood pressure and cholesterol now can help avoid irreversible damage later in life."

Mr Stavreski said younger adults needed to start thinking about their heart health, and not simply assume that heart disease is a risk only for those older than 50.

"There are many modifiable risk factors for heart disease that you can address before they contribute to full-blown heart disease in the future," Mr Stavreski said.

"While there are some risks you can't change - like age, sex, ethnicity and family history - there are other risks we can all take steps towards reducing, including maintaining a healthy weight, being physically active and smoke-free, and managing high blood pressure and high cholesterol."

Overall, close to four in five people aged 35-75 recorded a heart age higher than their actual age.

"This represents a staggering number of Australians who could be a ticking time bomb for a heart attack or stroke," Mr Stavreski said.

"It is encouraging that two million people have taken the heart age calculator to learn more about their risk for heart disease, but this is only the first step.

"If you are 18 or over, we recommended getting your blood pressure checked at least every two years, and your cholesterol at least every five years. If you're 45 and over, or from 30 for Aboriginal and Torres Strait Islander Australians, you should get these monitored as part of a regular heart health check."

The call comes after the Heart Foundation flagged a dramatic drop in heart health screenings during the pandemic.

"These heart age test results reinforce that Australians should not put off these checks any longer, particularly those who skipped appointments due to COVID-19," Mr Stavreski said.

"The good news is there's plenty you can do to reduce your risk for heart disease and lower your heart age. Your GP will support you in taking the necessary steps to improve your heart health, which may include changes to your diet, exercising, and possibly taking medications."

The calculator works by taking someone's answers about their age, sex, smoking and diabetes status, height and weight, cholesterol and blood pressure levels and if they take medication to control them, and whether close family members had a history of heart attack or stroke before age 60.

It provides a heart age, which is an initial indication of a person's overall risk for heart disease compared to a healthy range. A heart age that is older than a person's biological age may indicate higher risk of having a heart attack or stroke.

Try it out here