Even though the circulatory system looks like it's perfect, it isn't. There are problems to it. Heart attack, which is basically the heart failing, can be caused by diseases. Here are some examples of heart diseases:

Aortic Aneurysm is the swelling of the aorta. It is caused when the aorta wall is ripped.
Angina is physical suffering in the chest. It happens when blood vessels near the heart are blocked.
Arrhythmia is improper heart rhythm.
Atherosclerosis is when the artery wall hardens up.