The use of long-term aspirin can cause gastric bleeding, ulcers, supress the immune system and promote macular degeneration that causes blindness.

A study published in the British Medical Journal found that the risk of gastrointestinal haemorrhage (bleeding) with aspirin doesn't change, whether the dose you take is small or large. In other words, lowering your dose won't decrease the risk of this adverse affect, and while aspirin decreases the risk of some types of strokes, it also increases the risk of other types.

Aspirin essentially works by blocking the production of hormone-like substances called prostaglandins that regulate cells in the body in many of their complex interactions.

Prostaglandins are a group of fatty acids normally manufactured within the body. Prostaglandins act in a manner similar to that of hormones, as they stimulate their target cells into action. However, they also differ from hormones as they only act on cells locally where they are produced.

Some prostaglandins, when made in the body in excess, promote heart disease, inflammation and pain.

Aspirin very effectively blocks these protaglandins, which is good, except that aspirin will also block the formation of "good" prostaglandins that the body requires for normal function. This results in a supression of the immune system.

While the bad prostaglandins can make your blood more likely to aggregate or clump togetherand cause a stroke or heart attack:
good prostaglandins                   lower blood pressure
                                                inhibit blood stickiness
                                                inhibits the production of cholesterol
                                                reduce inflammatory reactions

Much of heart disease has to do with the fact that bad prostaglandins are outweighing good prostaglandins.

There are other natural substances we can use to prevent heart disease without aspirin's side effects. Most of the good prostaglandins are made from omega 3 oils, including DHA and EPA (found in deep-water fish) and alpha-linolenic acid (found abundantly in flaxseeds, walnuts and pumpkin seeds).