Electrocardiographic Studies of Dogs Infested with Dirofilaria immitis

Electrocardiograms were taken of 3 dogs uninfested and of 2 infested by Dirofilaria immitis. No significant differences were found. One normal and 2 infested dogs were then exercised moderately, electrocardiograms being recorded shortly before and immediately after running for 10 min. on a treadmill. In the normal dog and in one infested, exercise produced no significant changes. In the other dog, however, the QRS interval was slightly prolonged (0.04 to 0.05 sec.); the R wave amplitude was decreased in all leads (from 16.0 mm. to 10.5 mm. in lead II); and the T wave in lead I was inverted (from an amplitude of 1.0 mm. upward to 1.0 mm. downward), while in lead II, T changed from a height of 2 mm. to zero or isoelectric.