<prompt> True about cardiac O2 demand is-Directly proportional to mean arterial pressureInversely proportional to heart rateInversely proportional to cardiac workHas a constant relation to the external work done by the heart  <response>: Ans. a Directly proportional to mean arterial pressureRef: Ganong, 25th edp.612Myocardial oxygen consumption is directly proportional to mean arterial pressure 