Angina pain is not a heart attack. Angina pain means that some of the heart muscles have not been getting enough blood temporarily – for example, during exercise, when the heart has to work harder. The pain does NOT mean that the heart muscle is suffering irreversible, permanent damage.
A heart attack occurs when the blood flow to a part of the heart is suddenly and permanently cut off. This causes permanent damage to the heart muscle. Typically, the chest pain is more severe, lasts longer, and does not go away with rest or with medicine that was previously effective. It may be accompanied by indigestion, nausea, weakness, and sweating. However, the symptoms of a heart attack are varied and may be considerably milder.

Angina means that there is underlying coronary heart disease. Patients with angina are at an increased risk of heart attack compared with those who have no symptoms of cardiovascular disease, but the episode of angina is not a signal that a heart attack is about to happen. When the pattern of angina changes – if episodes become more frequent, last longer, or occur without exercise – the risk of heart attack in subsequent days or weeks is much higher.
A person who has angina should learn the pattern of his or her angina – what causes an angina attack, what it feels like, how long the episodes usually last, and whether medication relieves the attack. If the pattern changes sharply or if the symptoms are those of a heart attack, one should get medical help immediately, perhaps best done by seeking an evaluation at a nearby hospital emergency room

Difference Between “Stable” and “Unstable” Angina
“Stable” angina, the most common variety is one which occurs in a regular or characteristic pattern. Commonly, a person recognizes that he or she has been having angina only after several episodes have occurred, and a pattern has evolved. The level of activity or stress that provokes the angina is somewhat predictable, and the pattern changes only slowly.
"Unstable angina" needs prompt medical attention. Instead of appearing gradually, angina may first appear as a very severe episode or as frequently recurring bouts of angina. It can be provoked by far less exercise than in the past, or it may appear at rest.
The term “unstable angina” is also used when symptoms suggest a heart attack but hospital tests do not support that diagnosis. For example, a patient may have typical but prolonged chest pain and poor response to rest and medication, but there is no evidence of heart muscle damage either on the electrocardiogram or in blood enzyme tests.

There are two other forms of angina pectoris. One, is called Prinzmetal’s or variant angina. This type is caused by vasospasm, a spasm that narrows the coronary artery and lessens the flow of blood to the heart. The other is a recently discovered type of angina called microvascular angina. Patients with this condition experience chest pain but have no apparent coronary artery blockages. Microvascular angina can be treated with some of the same medications used for angina pectoris.