A cardiologist is a medical doctor who specializes in diagnosing and treating diseases related to the heart and blood vessels. They focus on conditions such as heart attacks, high blood pressure, heart failure, arrhythmias, and congenital heart defects. Cardiologists use various tests like ECG, echocardiograms, and stress tests to assess heart health. They also guide patients on lifestyle changes, medications, and procedures like angioplasty or bypass surgery when necessary. Some cardiologists further specialize in areas like interventional cardiology or electrophysiology.