The World Heart Federation said physical inactivity doubles the chances of developing heart disease and increases the risk of diabetes and high blood pressure.
The warning was issued ahead of World Heart Day on Sunday 29 September.
Doctors estimate that between 65% and 85% of the world's population fail to take enough exercise.
Professor Mario Maranhao, president of the World Heart Federation, said that children were also at risk.
Two out of three children around the globe take too little exercise to improve their health.
Health benefits
Professor Maranhao urged people to exercise.
"Even moderate exercise such as a brisk walk for 30 minutes most days helps control weight, cuts stress, anxiety and depression."
Professor Maranhao also advised people to improve their diet and to eat plenty of fruit, grains and vegetables and reduce their intake of alcohol and saturated fats.
Around 90 countries are expected to take part in World Heart Day which will feature events such as carnivals, walks, shows, public talks, sports tournaments and exhibitions.
The event is being supported by Brazilian footballer Ronaldo and Chow Yun Fat, star of the Oscar-winning film Crouching Tiger Hidden Dragon.
Ronaldo, who is a United Nations Development Programme Goodwill Ambassador, backed calls for people to exercise more.
He said: "Wherever you live in the world, there is no substitute for moderate but regular exercise and with a small amount of effort you can make a big difference."
Actor Chow Yun Fat exercises five times a week and eats mainly rice, fish and vegetables.
His belief in the benefits of healthy lifestyle has led to him becoming a goodwill ambassador for the World Heart Federation and supporting World Heart Day.
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