The authors studied the ECGs of 21 boys with Duchenne's progressive muscular dystrophy (group D) aged from 8 months to 10.5 years. They were compared with 21 age matched healthy boys. There were no statistical significant differences between both groups on maximal or minimal heart rates, nor on their subtractions. There were no differences between the electrical axis of P, QRS or T waves in the frontal plane, nor in the duration or amplitude of P waves. R wave in V1 had 1.06 +/- 0.38 (mean +/- 1 standard deviation) mV in group D, and 0.62 +/- 0.29 mV in group C (p less than 0.001). R/S ratio in V1 was 1.24 +/- 0.53 in group D, and 0.70 +/- 0.50 in group C (p less than 0.01). Q wave in V6 had 0.27 +/- 0.18 mV in group D, and 0.13 +/- 0.09 mV in group C (p less than 0.01). Q/R ratio in V6 was 0.19 +/- 0.14 in group D, and 0.09 +/- 0.047 in group C (p less than 0.01). Sensibility, specificity, positive predictive value, and negative predictive values for signs over 75 percentile (Davignon standards) were: for R wave in V1 71.4%, 76.2%, 75%, and 72.7%; for R/S ratio in V1 71.4%, 76.2%, 75% and 72.7%; for Q wave in V6 38.1%, 85.7%, 72.7%, and 58%.