Heart defects usually develop while a baby is still in the womb. About a month after conception, the heart begins to develop. It's at this point that heart defects can begin to form. Researchers aren't sure exactly what causes defects to begin, but they think some medical conditions, medications and genetics may play a role.

Causes of cardiomyopathy
The exact cause of cardiomyopathy, a thickening or enlarging of the heart muscle, is unknown. There are three types of cardiomyopathy:

* Dilated cardiomyopathy. This is the most common type of cardiomyopathy. In this disorder, your heart's main pumping chamber — the left ventricle — becomes enlarged (dilated), its pumping ability becomes less forceful, and blood doesn't flow as easily through the heart.
* Hypertrophic cardiomyopathy. This type involves abnormal growth or thickening of your heart muscle, particularly affecting the muscle of your heart's main pumping chamber. As thickening occurs, the heart tends to stiffen and the size of the pumping chamber may shrink, interfering with your heart's ability to deliver blood to your body.
* Restrictive cardiomyopathy. The heart muscle in people with restrictive cardiomyopathy becomes stiff and less elastic, meaning the heart can't properly expand and fill with blood between heartbeats. It's the least common type of cardiomyopathy and can occur for no known reason.

Causes of heart infections
Heart infections, such as pericarditis, endocarditis and myocarditis, are caused when an irritant, such as a bacteria, virus or chemical, reaches your heart muscle. The most common causes of heart infections include:

* Bacteria. Endocarditis can be caused by a number of bacteria entering your bloodstream. The bacteria can enter your bloodstream through everyday activities, such as eating or brushing your teeth, especially if you have poor oral health. Myocarditis can also be caused by a tick-borne bacterium that is responsible for Lyme disease.
* Viruses. Heart infections can be caused by viruses, including some that cause influenza (coxsackievirus B and adenovirus), a rash called fifth disease (human parvovirus B19), gastrointestinal infections (echovirus), mononucleosis (Epstein-Barr virus) and measles (rubella). Viruses associated with sexually transmitted infections also can travel to the heart muscle and cause an infection.
* Parasites. Among the parasites that can cause heart infections are Trypanosoma cruzi, toxoplasma, and some that are transmitted by insects and can cause a condition called Chagas' disease.
* Medications that may cause an allergic or toxic reaction. These include antibiotics, such as penicillin and sulfonamide drugs, as well as some illicit substances, such as cocaine. The needles used to administer medications or illicit drugs also can transmit viruses or bacteria that can cause heart infections.
* Other diseases. These include lupus, connective tissue disorders, inflammation of blood vessels (vasculitis), and rare inflammatory conditions, such as Wegener's granulomatosis.

Causes of valvular heart diseases
There are many causes of diseases of your heart valves. Four valves within your heart keep blood flowing in the right direction. You may be born with valvular disease, or the valves may be damaged by such conditions as rheumatic fever, infections (infectious endocarditis), connective tissue disorders, and certain medications or radiation treatments for cancer.

Link:

http://www.mayoclinic.com/health/heart-disease/DS01120/METHOD=print