The sequence of normal recovery of excitability in the dog heart.

The sequence with which 18 to 70 ventricular sites recovered excitability after normal excitation was determined in 15 dogs. At the epicardial level the recovery sequence was similar to that of normal activation. The sequence of excitation and recovery differed at the endocardium with some basal areas recovering excitability earlier than the apex despite later activation. Evidence of a normal epicardial to endocardial recovery sequence was also obtained. The findings are compatible with and provide a tentative explanation of some features of T waves in human body surface electrocardiograms.