Isolated Langendorff-perfused rat hearts (n = 6/group) were subjected to 60, 90, 120, or 180 min of
ischemia with or without a 2-min preischemic infusion with
St. Thomas' Hospital cardioplegic solution that had been modified to contain concentrations of
calcium of 0, 0.5, 0.8, 1.0, 1.2, 1.8, or 2.4 mM. In general, irrespective of the
calcium concentration, hearts in the
cardioplegia group recovered better than those in the noncardioplegia group. There was no consistent relationship between
calcium content and postischemic recovery of function or
enzyme leakage after any of the durations of
ischemia studied. However, as expected, there was a strong inverse relationship between recovery and duration of
ischemia. The recovery of function correlated with
enzyme leakage but not with the time to onset or magnitude of
ischemic contracture. In conclusion, although the neonatal rat heart benefits from
cardioplegia the protection is less impressive than that reported for adult hearts. Nonetheless, the neonatal heart appears to be very resistant to
ischemia. We propose that many of these differences can be explained on the basis of differences in myocardial
calcium handling between neonate and adult.