▁was ▁two fold . ▁First , ▁radio active ▁subst ances ▁could ▁be ▁used ▁to ▁determine ▁card iac ▁phys i ology ▁( function ) ▁and ▁should ▁be ▁done ▁so ▁with ▁the ▁least ▁amount ▁of ▁radio activity ▁necessary ▁to ▁do ▁so . ▁Second ly , ▁to ▁accomplish ▁this ▁task , ▁one ▁needs ▁to ▁obtain ▁multiple ▁counts ▁over ▁time . ▁ ▁For ▁dec ades ▁no ▁substantial ▁work ▁was ▁done , ▁until ▁ 1 9 5 9 . ▁Dr . ▁Richard ▁Gor lin ' s ▁work ▁on ▁" rest ing " ▁studies ▁of ▁the ▁heart ▁and ▁nit rog ly cer in ▁emphas ized ▁several ▁points . ▁ ▁First , ▁like ▁Bl um gart , ▁he ▁emphas ized ▁that ▁evaluation ▁of ▁card iac ▁function ▁required ▁multiple ▁measurements ▁of ▁change ▁over ▁time ▁and ▁these ▁measurements ▁must ▁be ▁performed ▁under ▁same ▁state ▁conditions , ▁without ▁changing ▁the ▁function ▁of ▁the ▁heart ▁in ▁between ▁measurements . ▁ ▁If ▁one ▁is ▁to ▁evaluate ▁is chem ia ▁( redu ctions ▁in ▁coron ary ▁blood ▁flow ▁resulting ▁from ▁coron ary ▁ar tery ▁disease ) ▁then ▁individuals ▁must ▁be ▁studied ▁under ▁" str ess " ▁conditions ▁and ▁compar isons ▁require ▁" str ess - str ess " ▁compar isons . ▁ ▁Similarly , ▁if ▁t issue ▁damage ▁( heart ▁attack , ▁my oc ard ial ▁inf ar ction , ▁card iac ▁st unning ▁or ▁hi bern ation ) ▁is ▁to ▁be ▁determined , ▁this ▁is ▁done ▁under ▁" rest ing " ▁conditions . ▁ ▁Rest - str ess ▁compar isons ▁do ▁not ▁yield ▁ade qu