New research says that a far better way of assessing a persons heart attack risk is to look at waist-to-hip ratio rather than a person's relative height and weight.
Currently many experts use a Body Mass Index (BMI) as the standard tool for judging if someone is at risk from being overweight.
A person's BMI is worked out by multiplying weight in kilograms by height in metres squared.
A BMI of 20 to 25 is considered normal, 25 to 30 overweight, and over 30 obese.
Now however, according to the researchers, a larger waist size was found to be harmful, whereas larger hip size - possibly indicating lower-body muscle mass - was protective.
The researchers, led by Professor Salim Yusuf, from Hamilton General Hospital in Ontario, Canada, found that measuring waist-to-hip ratio was three times better at predicting the risk of heart attack than BMI.
The danger point was more than 0.85 for women and more than 0.9 for men, and this is because fat stored around the waist is more likely to affect lipids in the blood and clog up arteries than fat stored around the thighs and hips.
In other words, apple-shaped people are more at risk of heart problems than those who are pear-shaped.
A greater risk of heart attack is often associated with a high BMI, but now researchers say that measure could be giving a false picture of the dangers of being overweight.
Furthermore, if obesity is redefined using WHR instead of BMI, the proportion of "abdominally obese" people at risk of heart attack increases by three-fold, according to the researchers.
Yusuf's team examined BMI, waist-to-hip ratio, and waist and hip measurements in more than 27,000 people from 52 countries.
Of the participants, half had previously had a heart attack, while the other half had no history of heart attacks, but were the same age and sex.
They say a better system is to measure the relative size of waist and hips, which focuses on abdominal fat.
Waist and hip circumference were recorded using a standard tape measure.
For the waist measurement, it was stretched around the unclothed abdomen, and hips were measured at the level of the widest diameter around the buttocks.
The researchers found that BMI was only slightly higher in heart attack patients than in controls, with no difference for people from the middle east and southern Asia.
They also say that the global burden of obesity has been substantially underestimated by the reliance of BMI in previous studies.
The study is published in the current edition of The Lancet medical journal.