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By a 3M KCI glass microelectrode, transmembrane potentials were recorded in the compact and transitional areas bounded by superior, inferior vena cava and left, right, atria. The results were as followings: 1. In 35℃, normal Tyrode solution, the beating frequency, maximum diastolic potential (M.D.P.) and overshoot potential (O.P.) in the compact and transitional areas were 180±17/min. and 210±19/min., -76±3.7㎷ and -73±2.4㎷, 15±2.9㎷ and 19±2.8㎷ respectively which showed the transitional area was faster, and showed more positive M.D.P., more positive O.P. 2. Adrenaline made the transitional area more sensitively the frequency faster, more steeper the pacemaker potential, more positive the overshoot potential. 3. Tetrototoxin (TTX) has been found to be more sensitive on the transitional area to be less steeper the slope of pacemaker potential and the frequency slower. 4. Blocking the calcium current by 2mM Mn^2+ made the compact area, more sensitively and sometimes irreversible to reduce the beating frequency, overshoot potential and M.D.P.
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