The esophageal electrocardiogram is of increasing significance in the study and diagnosis of cardiac arrhythmia and of posterior myocardial disease. We used both bipolar and unipolar esophageal recording leads and standard electrocardiogram equipment, and compared the effectiveness of esophageal electrocardiogram with co nventional electrocardiogram. The effectiveness of esophageal electrocardiogram were as follows: 1) Differentiation of sinus, atrial, junctional, or ventricular rhythm. 2) Differentiation of origin of premature beats. 3) Differentiation of atrial flutter and fibrillation. 4) Detection of retrograde atrial conduction of extraventricular systole. 5) Detection of electrical alternance of QRS amplitude. 6) Diagnosis of posterior myocardial infarction. The results reported here indicate that the esophageal electrocardiogrm seems to be a valid method in the diagnosis of cardiac arrhythmias without invasiveness.