Let's take a look at the literature on this one. The worldwide INTERHEART study, published in the medical journal The Lancet in 2004 demonstrated that the majority of risk factors for heart disease are "modifiable," meaning they are factors you can change about yourself or your behavior (as opposed to non-modifiable risk factors like age, gender, race, etc). In fact, nine of these modifiable risk factors were responsible for a startling 90 percent of the risk of developing heart disease. The risk factors included: smoking, blood cholesterol levels, abdominal obesity (greater than 40" for men or 35" for women), daily physical activity, high blood pressure, diabetes, dietary consumption of fruits and vegetables, moderate alcohol intake and psychosocial factors.
More specifically, there is a preponderance of evidence in the medical literature to show that a diet high in fruits and vegetables and fiber and low in saturated fats is protective against stroke and heart disease. Regular, moderate alcohol consumption also plays a protective role. However, overindulgence is a concern as are the attendant increased risks of certain types of cancer at the higher end of the intake spectrum. Interesting, epidemiologic studies have shown that people who consume more fish are at lower risk of heart disease.
A final point: an active lifestyle is not a blank check in terms of diet. Not only can heart disease still develop if you're a weekend warrior triathlete who feasts on ribs and fries, but there are a number of other factors at play- both modifiable and non-modifiable- including family history, race, gender and age. It's better to fight the battle on all possible fronts.