(a) Competent principal. -- A principal of sound mind may countermand any health care decision made by the principal's health care agent at any time and in any manner by personally informing the attending physician or health care provider.

(b) Incompetent principal. -- Regardless of the principal's mental or physical capacity, a principal may countermand a health care decision made by the principal's health care agent that would withhold or withdraw life-sustaining treatment at any time and in any manner by personally informing the attending physician.

(c) Attending physician. -- The attending physician or health care provider shall make reasonable efforts to promptly inform the health care agent of a countermand under this section.

(d) Health care agent. -- A countermand exercised under this section shall not affect the authority of a health care agent to make other health care decisions in accordance with the health care power of attorney.