While heart attacks can occur at any time, most heart attacks occur between 4:00 A.M. and 10:00 A.M. because of the higher blood levels of adrenaline released from the adrenal glands during the morning hours. Increased adrenaline, as previously discussed, may contribute to rupture of cholesterol plaques.

Approximately 50% of patients who develop heart attacks have warning symptoms such as exertional angina or rest angina prior to their heart attacks.

What are the symptoms of a heart attack?

Although chest pain or pressure is the most common symptom of a heart attack, heart attack victims may experience a diversity of symptoms that include:

 
• Pain, fullness, and/or squeezing sensation of the chest  
• Jaw pain, toothache, headache  
• Shortness of breath  
• Nausea, vomiting, and/or general epigastric (upper middle abdomen) discomfort  
• Sweating  
• Heartburn and/or indigestion  
• Arm pain (more commonly the left arm, but may be either arm)  
• Upper back pain  
• General malaise (vague feeling of illness)  
• No symptoms (Approximately one quarter of all heart attacks are silent, without chest pain or new symptoms. Silent heart attacks are especially common among patients with diabetes mellitus)

Even though the symptoms of a heart attack at times can be vague and mild, it is important to remember that heart attacks producing no symptoms or only mild symptoms can be just as serious and life-threatening as heart attacks that cause severe chest pain. Too often patients attribute heart attack symptoms to “indigestion,” “fatigue,” or “stress,” and consequently delay seeking prompt medical attention. One cannot overemphasize the importance of seeking prompt medical attention in the presence of symptoms that suggest a heart attack. Early diagnosis and treatment saves lives, and delays in reaching medical assistance can be fatal. A delay in treatment can lead to permanently reduced function of the heart due to more extensive damage to the heart muscle. Death also may occur as a result of the sudden onset of arrhythmias such as ventricular fibrillation.

What are the complications of a heart attack?

Heart failure

If a large amount of heart muscle dies, the ability of the heart to pump blood to the rest of the body is diminished, and this can result in heart failure. The body retains fluid, and organs, for example, the kidneys, begin to fail

ventricular fibrillation

Injury to heart muscle also can lead to ventricular fibrillation. ventricular fibrillation occurs when the normal, regular, electrical activation of heart muscle contraction is replaced by chaotic electrical activity that causes the heart to stop beating and pumping blood to the brain and other parts of the body. Permanent brain damage and death can occur unless the flow of blood to the brain is restored within five minutes.

Most of the deaths from heart attacks are caused by ventricular fibrillation of the heart that occurs before the victim of the heart attack can reach an emergency room. Those who reach the emergency room have an excellent prognosis; survival from a heart attack with modern treatment should exceed 90%. The 1% to 10% of heart attack victims who die later include those victims who suffer major damage to the heart muscle initially or who suffer additional damage at a later time.

Deaths from ventricular fibrillation can be avoided by Cardiopulmonary resuscitation (CPR) started within five minutes of the onset of ventricular fibrillation. CPR requires breathing for the victim and applying external compression to the chest to squeeze the heart and force it to pump blood. When paramedics arrive, medications and/or an Electrical shock (cardioversion) can be administered to convert ventricular fibrillation back to a normal heart rhythm and allow the heart to pump blood normally. Therefore, prompt CPR and a rapid response by paramedics can improve the chances of survival from a heart attack. In addition, many public venues now have defibrillators that provide the Electrical shock needed to restore a normal heart rhythm even before the paramedics arrive. This greatly improves the chances of survival.

What are the risk factors for atherosclerosis and heart attack?

Factors that increase the risk of developing atherosclerosis and heart attacks include increased blood cholesterol, high blood pressure, use of tobacco, diabetes mellitus, male gender, and a family history of coronary heart disease. While family history and male gender are genetically determined, the other risk factors can be modified through changes in lifestyle and medications.

 
• High Blood Cholesterol (Hyperlipidemia). A high level of cholesterol in the blood is associated with an increased risk of heart attack because cholesterol is the major component of the plaques deposited in arterial walls. Cholesterol, like oil, cannot dissolve in the blood unless it is combined with special proteins called lipoproteins. (Without combining with lipoproteins, cholesterol in the blood would turn into a solid substance.) The cholesterol in blood is either combined with lipoproteins as very low-density lipoproteins (VLDL), low-density lipoproteins (LDL) or high-density lipoproteins (HDL).     The cholesterol that is combined with low-density lipoproteins (LDL cholesterol) is the “bad” cholesterol that deposits cholesterol in arterial plaques. Thus, elevated levels of LDL cholesterol are associated with an increased risk of heart attack.     The cholesterol that is combined with HDL (HDL cholesterol) is the “good” cholesterol that removes cholesterol from arterial plaques. Thus, low levels of HDL cholesterol are associated with an increased risk of heart attacks.     Measures that lower LDL cholesterol and/or increase HDL cholesterol (losing excess weight, diets low in saturated fats, regular exercise, and medications) have been shown to lower the risk of heart attack. One important class of medications for treating elevated cholesterol levels (the statins) have actions in addition to lowering LDL cholesterol which also protect against heart attack. Most patients at “high risk” for a heart attack should be on a statin no matter what the levels of their cholesterol. For more, please see the Cholesterol and Your Heart article.  
• High Blood Pressure (Hypertension). High blood pressure is a risk factor for developing atherosclerosis and heart attack. Both high systolic pressure (when the heart beats) and high diastolic pressure (when the heart is at rest) increase the risk of heart attack. It has been shown that controlling hypertension with medications can reduce the risk of heart attack. For more, please see the High Blood Pressure article.  
• Tobacco Use (Smoking). Tobacco and tobacco smoke contain chemicals that cause damage to blood vessel walls, accelerate the development of atherosclerosis, and increase the risk of heart attack. For more, please see the Smoking and Quitting Smoking article.  
• Diabetes (Diabetes Mellitus). Both insulin dependent and non-insulin dependent diabetes mellitus (type 1 and 2, respectively) are associated with accelerated atherosclerosis throughout the body. Therefore, patients with diabetes mellitus are at risk for reduced blood flow to the legs, coronary heart disease, erectile dysfunction, and strokes at an earlier age than non-diabetic subjects. Patients with diabetes can lower their risk through rigorous control of their blood sugar levels, regular exercise, weight control, and proper diets. For more, please see the Diabetes article.  
• Male Gender. At all ages, men are more likely than women to develop atherosclerosis and coronary heart disease. Some scientists believe that this difference is partly due to the higher blood levels of HDL cholesterol in women than in men. However, this gender difference narrows as men and women grow older.  
• Family History of Heart Disease. Individuals with a family history of coronary heart diseases have an increased risk of heart attack. Specifically, the risk is higher if there is a family history of early coronary heart disease, including a heart attack or sudden death before age 55 in the father or other first-degree male relative, or before age 65 in the mother or other female first-degree female relative.