I am trying to build medical word that corresponds to this definition.

Pertaining to the heart and lung cavity is what?

heart = cardi-

http://www.answers.com/topic/cardio

lungs = pulmonary
http://www.answers.com/topic/pulmonary

The medical word that corresponds to the definition "pertaining to the heart and lung cavity" is "cardiopulmonary."

To arrive at this answer, you can break down the definition into its components:

1. "Pertaining to" means related to or concerning a specific area or topic. In medical terminology, it is represented by the prefix "cardio-" or "cardi-," which refers to the heart, and "pulmonary," which refers to the lungs.

2. "Heart" in medical terminology is represented by the prefix "cardio-" or "cardi-."

3. "Lung" in medical terminology is represented by the prefix "pulmo-".

By combining these components, we get "cardiopulmonary," which specifically relates to the heart and lung cavity.