Scientists monitored the health of more than 2,500 Greek adults aged 18 to 89 over a 10-year period between 2001 and 2012.
They found that those who closely adhered to a traditional Mediterranean diet were 47% less likely to develop heart disease than those who did not.
Researcher Ekavi Georgousopoulou, from Harokopio University in Athens, said: "Our study shows that the Mediterranean diet is a beneficial intervention for all types of people - in both genders, in all age groups, and in both healthy people and those with health conditions.
"It also reveals that the Mediterranean diet has direct benefits for heart health, in addition to its indirect benefits in managing diabetes, hypertension (high blood pressure) and inflammation."
The scientists scored participants' diets on a scale from one to 55 based on their consumption of 11 food groups.
Each one-point increase in dietary score, corresponding to a more complete Mediterranean diet, was associated with a 3% drop in heart disease risk.
Earlier research has linked the Mediterranean diet to weight loss, a reduced risk of diabetes, lower blood pressure and lower blood cholesterol levels.
"Because the Mediterranean diet is based on food groups that are quite common or easy to find, people around the world could easily adopt this dietary pattern and help protect themselves against heart disease with very little cost," said Georgousopoulou.
He stressed that although Greeks might be expected to follow a Mediterranean diet, urbanisation had led many of them to adopt more Western tastes over the past four decades.
The findings were presented at the American College of Cardiology's 64th Annual Scientific Session in San Diego, California.