1.1. In the electrocardiograms of 709 apparently normal college students, no significant Q-3 waves were discovered. Among 117 college athletes, the only significant Q-3 wave occurred in an individual with rheumatic heart disease.2.2. A significant Q-3 wave was found in approximately 6 per cent of 500 hospital, ward and clinic patients with cardiovascular disease. Although all ages were included, the youngest patient to show a significant Q-3 wave was thirty-two years of age; the oldest was seventy-two years. Hypertension, arteriosclerosis and syphilis were regarded as the etiological factors of the heart disease in the majority of cases, but significant Q-3 waves were also seen in cases of rheumatic and thyrotoxic heart disease.3.3. In nineteen hundred unselected electrocardiograms taken from the files of the Cardiographic Laboratory, including ward, clinic and private patients of all ages, there were 78 (4.1 per cent) significant Q-3 waves. Of the 78 individuals exhibiting the significant Q-3 waves, 63 were classified as having heart disease, 7 were placed in a doubtful group, 5 were considered negative, and 3 were not classified because of inadequate records.4.4. Thirty-one or 26.7 per cent of one hundred and sixteen cases of the anginal syndrome showed a significant Q-3 wave.5.5. Eight or 5.5 per cent of the electrocardiograms of one hundred and forty-five corporation executives showed a significant Q-3 wave. In seven of these eight cases there was definite evidence of cardiovascular disease, although the history in all was negative.6.6. A total of 149 significant Q-3 waves was found in the first five groups of this study. The electrocardiogram was otherwise normal in 68 cases; 64 showed T-wave changes; and 17 other electrocardiographic abnormalities. This sign, therefore, may constitute the first electrocardiographic change to invite attention to the possibility of cardiac damage.7.7. Twenty-five pregnant women in the ninth month, were electrocardiographed, and three were found to show significant Q-3 waves. In two of these who were reexamined, several months after delivery, the Q-3 wave had vanished.8.8. Available evidence indicates that the conditions chiefly responsible for deep Q-3 waves are either (1) a lesion of the septum which interferes with the spread of the excitatory process, or (2) deviation of the septum from its usual position with reference to Lead III of the electrocardiogram.9.9. Study of the clinical incidence of the deep Q-3 wave suggests that in the majority of cases change of position rather than injury severe enough to alter the spread of the excitatory process, is the important factor in the production of this wave.10.10. Deep Q-3 waves which conform to the criteria of Pardee are occasionally present in electrocardiograms of patients who show neither evidence of cardiac disease nor changes from the normal in the size and position of the heart. Whether or not this is due to some peculiarity in the ventricular tissues first invaded by the excitatory process, cannot be stated. It is important, however, to take these cases into account when the attempt is made to evaluate the clinical significance of the deep Q-3 wave.

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   |texte=   The incidence and significance of the deep Q-wave in Lead III of the electrocardiogram
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