Pacing-induced heart failure in the dog recapitulates many of the electrophysiological and
hemodynamic abnormalities of the human disease; however, the mechanisms underlying
altered Ca2+ handling have not been investigated in this model. We now show that left
ventricular midmyocardial myocytes isolated from dogs subjected to 3 to 4 weeks of rapid
pacing have prolonged action potentials and Ca2+ transients with reduced peaks, but
durations≈ 3-fold longer than controls. To discriminate between action potential effects on …

Ca2+ transients measured in failing human ventricular myocytes exhibit reduced amplitude,
slowed relaxation, and blunted frequency dependence. In the companion article (O'Rourke
B, Kass DA, Tomaselli GF, Kääb S, Tunin R, Marbán E. Mechanisms of altered excitation-
contraction coupling in canine tachycardia-induced heart, I: experimental studies. Circ Res.
1999; 84: 562–570), O'Rourke et al show that Ca2+ transients recorded in myocytes isolated
from canine hearts subjected to the tachycardia pacing protocol exhibit similar responses …