<prompt> True regarding myocardial 02 demandInversely related to hea rateHas constant relation to external cardiac workDirectly propoional to duration of systoleIs negligible at rest  <response>: Experimental studies have shown that oxygen consumption of the hea and the chemical energy expended during contraction are directly related to the external work Ref: Guyton and Hall Textbook of Medical Physiology 12th Edn page No:209 