From the BBC:
For those drinking little – less than a shot of vodka a day for instance – the risk was reduced by 35%. And for those who drank anything from three shots to more than 11 shots each day, the risk worked out an average of 50% less.
The same benefits were not seen in women, who suffer fewer heart problems than men to start with. Researchers speculated this difference could be down to the fact that women process alcohol differently, and that female hormones protect against the disease in younger age groups.
The type of alcohol drunk did not seem to make a difference, but protection was greater for those drinking moderate to high amounts of varied drinks.
The exact mechanisms are as yet unclear, but it is known that alcohol helps to raise high-density lipoproteins, sometimes known as good cholesterol, which helps stop so-called bad cholesterol from building up in the arteries.
More here.