Cardiology is the branch of medicine that deals with the study and treatment of diseases and disorders affecting the heart and arteries.

What does a cardiologist do?

A cardiologist is concerned with the diagnosis, treatment, and cure of diseases that affect the heart and arteries. It is not a cardiologists duty to surgically intervene to resolve issues. In this case a cardiologists will refer the patient to a heart surgeon.

What diseases are treated by a cardiologist?

Among the diseases often treated by a cardiologist are ischemic cardiomyopathy (heart attack), heart failure, angina pectoris, hypertension, arrhythmias, congenital heart defects, CHD, and atherosclerosis. 

What are the procedures used by a cardiologist? 

A cardiologist will gather a medical history of the patient, followed by a physical examination that includes listening to the heart and conducting an electrocardiogram (ECG).
The doctor can ask for more test to be conducted if the diagnosis is unclear such as a doppler echocardiography, carotid ultrasound, respirator fit test, holter monitor, spect scan, and electrophysiological studies. 
A cardiologist can decide that the most appropriate treatment is a surgery such as angioplasty, valvuloplasty, congenital malformation interventions, and thrombectomy which will be performed by a heart surgeon. 

When should a patient visit a cardiologist?

It is recommended to seek an appointment with a cardiologist whenever a patient feels symptoms involving the heart, and after consulting with a general practitioner. Among the issues that raise concern are high cholesterol levels or high blood pressure, pain and discomfort in the chest, shoulders, neck, arms or jaw, especially if they tend to worsen or if they are associated with intense sweating, paleness, vomiting, dizziness, and fainting. Other issues include irregular heartbeat and low blood pressure. 
The visit is also recommended in case of a family history of cardiovascular problems and in the case of diabetes and preeclampsia. Finally, it is recommended to conduct a visit if a patient is a smoker or is starting a new type of physical activity after the age of 40.