The problem is twofold: Americans are eating too much salty, fatty and sugary fare, and not enough fruit, vegetables and whole grains, experts said at a meeting of the American Heart Association in Portland, Oregon.
"Low intake of healthy foods such as nuts, vegetables, whole grains and fruits combined with higher intake of unhealthy dietary components, such as salt and trans fat, is a major contributor to deaths from cardiovascular disease in the United States," said lead study author Mr Ashkan Afshin, assistant professor of global health at the University of Washington's Institute for Health Metrics and Evaluation.
Trans fat has been largely phased out of the food supply, but can still be found in some margarines, biscuits, cookies, frosting and other processed foods.
If Americans were to alter their eating habits, many lives could be saved, Mr Afshin said.
"Our results show that nearly half of cardiovascular disease deaths in the United States can be prevented by improving diet."
The study was based on data from a variety of sources going back to the 1990s, including the National Health and Nutrition Examination Survey and the Food and Agriculture Organization of the United Nations.
More than 600,000 people die annually because of heart disease, or one in four of all US deaths.
Smoking, obesity, diet, exercise and hereditary factors can all contribute to person's likelihood of developing heart disease.
By examining data on US cardiovascular deaths in 2015, researchers found that dietary choices played a role in the deaths of an estimated 222,100 men and 193,400 women.
Experts at the American Heart Association encourage people to eat a diet rich in fruits, vegetables, nuts, beans, whole grains, low-fat dairy products, fish and poultry.
People should avoid or limit their intake of fatty or processed red meat, sugary soft drinks, salt, saturated and trans fats.