Vitamin D is not a true vitamin since we can manufacture it in our bodies, through the action of UVB rays through the skin which convert 7-dehydrocholesterol to vitamin D. We can also get it through foods and supplements as vitamin D2 (ergocalciferol or pre-vitamin D) or vitamin D3 (cholecalciferol).
Age, obesity, dark skin, chronic disease and lack of exposure to the sun - or use of sunscreen - limit your body's ability to manufacture vitamin D. Most adults, particularly the further north they live, are vitamin D deficient if they don't take supplements. One probably needs more than 800 IU of D3 a day.
It is thought that vitamin D may help cardiovascular health in a variety of ways. Some of the proposed mechanisms include glycemic (blood sugar) control, helping blood vessel compliance (keep vessels more flexible), lowering blood pressures, and acting as an anti-inflammatory.
There does seem to be an association between vitamin D levels and heart disease. In the Health Professional Follow Up Study, vitamin D levels were measured in 50,000 healthy men, who were then followed for 10 years. The vitamin D deficient men were 2x more likely to have a heart attack. However, association does not prove causality. It very well could be that the thing(s) that lead to vitamin D deficiency also lead to coronary disease.
The Women's Health Initiative studied 36,282 post-menopausal women who were given either placebo or a combination of calcium carbonate 500 mg and vitamin D 200 IU twice a day. Over seven years, there was no difference in the incidence of coronary or cerebrovascular events. It may be that the dose of vitamin D was too low to be effective.
I have followed recommendations and trends in dietary advice and supplements with great interest over the past 25 years. What we think is a healthy diet now is much different from what we thought a decade or two ago. There has been great enthusiasm for vitamin E, beta-carotene, vitamin C and vitamin A at times over the past 20 years, and all have failed to live up to their early promise and are no longer recommended as supplements.
I do recommend that you get your vitamin D level checked, and take 1,000 or 2,000 IU a day, assuming you are deficient. There is no evidence that those doses are harmful in any way. I am taking my vitamin D daily.
However, don't forget to do all the other probably more important things to prevent heart problems in the future. Don't smoke. Exercise regularly. Keep your blood pressure in the normal range. Eat a healthy diet, low in sugars and simple carbs, with good proteins, high fiber, fruits, vegetables, and monounsaturated fats. Keep your cholesterol low if you are at risk.