We analyzed total Ca handling of the left ventricle (LV) in the mildly fail
ing heart preparation induced by a temporary intracoronary Ca overloading i
ntervention in eight excised and cross-circulated canine hearts. This Ca in
tervention consisted of interruption of coronary blood perfusion by Ca-free
oxygenated Tyrode perfusion for 10 min followed by high-Ca (16 mmol/l) oxy
genated Tyrode perfusion for 5 min. This intervention decreased the LV cont
ractility index, E-max (end-systolic maximum elastance), by 40% after resto
ration of the blood cross-circulation. We expected a Ca overload or paradox
failing heart resembling the postischemic stunned heart and being characte
rized by an increased O-2 cost of E-max. However, LV O-2 consumption under
mechanically unloading conditions decreased by 30% from control without inc
reasing the O-2 cost Of E-max. To Obtain a mechanistic view of this failing
heart, we investigated cardiac total Ca handling by our integrative analys
is method. In this method, we obtained the internal Ca recirculation fracti
on (RF) from the decay beat constant of the postextrasystolic potentiation
following each sporadic spontaneous extrasystole in these failing LVs. We c
ombined the RF with the decreased E-max and the unchanged O-2 cost of E-max
in our recently developed formula of total Ca handling. We found that thes
e failing LVs had a slightly but significantly increased RF accompanied by
either a slightly increased futile Ca cycling or a slightly decreased Ca re
activity of E-max, or both. Any of these three possible changes can account
for the unchanged O-2 cost of E-max. This result indicates that the presen
t mildly failing heart has not yet fallen into a typical Ca overload or par
adox by the temporary Ca overloading intervention.