The arterial pulse wave velocity was measured in 87 healthy individuals and in 52 diabetic patients who did not have clinical evidence of atherosclerosis or hypertension. A significant increase in the pulse wave velocity was found in the diabetic subjects. This increase was not correlated with the duration of their illness as judged from clinical history. It is very likely that the high values of pulse wave velocity were indicative of an incipient process of diffuse atherosclerosis and that the measurement of the pulse wave velocity brought this into evidence earlier than the classic signs and symptoms. Serial measurements of the pulse wave velocity in diabetic subjects may permit early detection of atherosclerosis in these patients.

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Transmembrane action potentials were recorded from embryonic rat hearts at ages between 10& days of gestation and birth (21 to 22 days). The resting potential averaged 30 to 40 mv at IOJ2 days and increased to around 80 mv by birth. Two periods of rapid increase in resting potential were noted: 1) from 10^ to 13& days and 2) from 19M days of gestation to birth. The maximal upstroke velocity of the action potential increased as the resting potential increased. The duration of the ventricular and atrial action potentials was inversely related to heart rate, and their rate sensitivity decreased with age. The atrial action potential lost its rate sensitivity by 13M days of gestation and the ventricular action potential lost its by birth. At IOJ2 days diastolic depolarization was found in the area of the ventricle proximate to the A-V junction, the left and right atria, and the sinus venosus. The velocity of the diastolic depolarization was greatest in the sinus venosus and least in the ventricle. The diastolic depolarization decreased with growth and was lost by 13/2 days of gestation. ADDITIONAL KEY WORDScardiac action potentials cardiac pacemaker cardiac electrophysiology diastolic depolarization mammalian embryonic heart growth and differentiation• The transmembrane action potential of the embryonic and fetal heart has been studied principally in the chick embryo (1-7).In the ventricle of 6-to 8-day chick embryo hearts, Lehmkuhl and Sperelalcis (2) found resting potentials of 72 mv and action potentials of 86 mv. Potentials in the range of 30 to 50 mv were found in 37-to 67-hour chick embryos by Meda and Ferroni (3). Action potential configuration was found to be simi-