A medical department (cardiology) that diagnoses and treats diseases of the heart and blood vessels (the circulatory system).
明日、循環器内科で心臓の検査を受けます。
I'm having a heart checkup at cardiology tomorrow.
彼は循環器内科の医師として長年働いている。
He has worked for many years as a cardiologist.
高血圧の患者は定期的に循環器内科を受診したほうがいい。
Patients with high blood pressure should see cardiology regularly.