A, maximal rate of rise of [Ca2+]i transients was substantially faster with ISO. Maximal rate of rise was also faster with increased SR loading, but this may be explained by the larger sizes of [Ca2+]i transients, as shown in B (data of A normalized to [Ca2+]i amplitude). C, ‘Rate gain’, i.e. maximal rate of rise normalized to ICa peak influx rate, was also higher with ISO. D, time at which maximal rate of rise (A) occurred was earlier with ISO. All comparisons: *P < 0.05.