Heart, circulatory system
Cardio- comes from Greek "kardia" (heart) and appears primarily in medical vocabulary. Cardiogram = graphic record of the heart; cardiology = the study of the heart; cardiovascular = of the heart and blood vessels; cardiac = relating to the heart; cardiopulmonary = of the heart and lungs. Spanish uses the identical prefix: cardiograma, cardiología, cardiovascular, cardíaco.