Dilated cardiomyopathy is associated with an increase in transverse plane QRS voltage but a decrease in frontal plane QRS voltage. To study this paradoxical relationship further, electrocardiograms (ECGs) were retrospectively analyzed from five groups of men. Frontal plane QRS voltage was computed as the sum of peak-to-trough QRS amplitudes in the two limb leads with highest QRS voltage; transverse QRS voltage as the maximum peak-to-trough QRS voltage in leads [V1 or V2] + [V5 or V6]. The transverse:frontal plane QRS voltage ratio was significantly (p less than 0.01) greater in 26 patients with idiopathic dilated cardiomyopathy (3.0 +/- 1.3) compared to 29 patients with compensated aortic valve disease (2.0 +/- 0.6), 30 healthy men (2.0 +/- 0.6) and 20 patients with ischemic heart disease and relatively normal left ventricular function (1.9 +/- 0.8), but not significantly different from the ratio for patients with ischemic cardiomyopathy (2.3 +/- 1.1). This differential effect of dilated cardiomyopathy on transverse and frontal plane QRS voltages, which probably relates to a combination of mechanical and vectorial factors, may be the basis of a useful new ECG sign.