View Notes - Chapter 18 Short Quiz Adaptive Follow-Up Set 1 from BIOL 1102 at Georgia State. 1. Which heart chamber receives oxygenated blood from the lungs? Left atrium 2. Which portion of the electrocardiogram represents the depolarization wave received by the atria from the sinoatrial (SA) mode? P wave 3. When an ectopic pacemaker leads to an extrasystole, the ventricles contract before the atria contract 4. The P wave on an electrocardiogram represents Atrial depolarization