Submit Manuscript | http://medcraveonline.com transients recorded with the Ca 2+ probe aequorin during isometric contraction of myocardium in patients with end-stage failure were markedly prolonged, with a peak and then a secondary peak in the [Ca 2+ ]i transient trace, which was associated with a marked prolongation of the time course of the Ca 2+ decline and of tension decline [2]. Because SERCA is responsible for 60% to 90% of the [Ca 2+ ]i decline in mammalian ventricular myocytes, these results were consistent with impaired function of the SR Ca 2+ transport