<prompt> Irreversible injury in myocardium occurs at ?2 minutes30 minutes2 hours5 hours  <response>: Ans. is b i.e., 30 minutes The metabolic rate of the hea is high, and its stores of substrate are low. So, hea is critically dependent on a continuous supply of oxygen and nutrients. Ischemia of myocardium induces profound functional, biochemical and morphological consequences. Myocardial function is more sensitive to isc_hemia loss of contractility occurs within 60 seconds than myocardial structure irreversible injury occurs in 20-40 minutes, thus myocardial necrosis begins at approximately 30 minutes after coronary occlusion. Key events in ischemic cardiac myocytes Feature Time Onset of ATP depletion Seconds Loss of contractility 2 minutes ATP reduced to 50 10 minutes ATP reduced to 10 40 minutes Irrversible injury 2040 min Microvascular injury 1 hr 