Cardiac means relating to the heart. When doctors talk about cardiac health, they mean how well your heart is working. A cardiac surgeon specializes in operating on hearts, and a cardiac arrest is when someone's heart suddenly stops beating.

You'll hear it most often in medical contexts: a hospital's cardiac unit treats patients with heart problems, and a cardiac monitor tracks heartbeats. Athletes training intensely might do cardio exercise to strengthen their hearts, helping them pump blood more efficiently.

You might also encounter the phrase cardiac muscle, which refers to the special type of muscle tissue that makes up the heart. Unlike the muscles in your arms that you control consciously, cardiac muscle works automatically, beating about 100,000 times every day without you thinking about it.

Scientists and doctors prefer cardiac over simply saying “heart” when they want to sound precise and medical, the same way they say pulmonary instead of “lung-related” or cerebral instead of “brain-related.”