Heart failure is a condition where the heart fails to pump and circulate an adequate supply of blood to meet the requirements of the body. The muscles of the heart become less efficient and damaged, leading to overload on the heart.

There are several conditions that can lead to heart failure. One example is heart muscle damage caused by a heart attack or myocardial infarction. In myocardial infarction, there is a lack of blood supplied to the heart muscles causing them to be starved of oxygen and leading to death of the muscle tissue. The muscles then fail to function normally, increasing the risk of heart failure.

Another example is anemia, in which there is inadequate oxygen delivery to important body parts meaning the heart has to work harder and is put under starin to pump more oxygen around the body. Cardiac muscle diseases such as amyloidosis or cardiomyopathy also damage the heart muscles and can lead to heart failure.

Some of the main pathologies of heart failure include:
 

• The muscle contraction of the heart may weaken due to overloading of the ventricle with blood during diastole. In a healthy individual, an overloading of blood in the ventricle triggers an increases in muscle contraction, to raise the cardiac output. This is called the Frank-Starling law of the heart. In heart failure, however, this mechanism fails due to weakened cardiac muscles which results in a failure of the heart to pump an adequate amount of blood.
• To compensate for the lowered cardiac output, the heart rate rises. This makes the condition worse as the heart muscles require more nutrients to work and the myocardial muscles pump at an increased rate.
• Stroke volume reduces as the systole or diastole contractions start to fail. If the volume of blood in the ventricle at the end of systole rises, it means less blood is ejected. If the volume at the end of diastole is decreased, it means less blood is entering the heart during diastole.
• The cardiac reserve may reduce. The heart needs to have the capacity to cope with normal metabolic demands as well as elevated demands, during exercise or exertion, for example. In heart failure, this reserve is lowered.
• With time, the heart starts to enlarge. This is called hypertrophy. Initially the heart muscle fibres increase in size to improve contractility but with time they become too stiff and unyielding to be of any benefit. The blood pressure in the arteries fall and there is reduced blood flow to the kidneys.