1. The Beating Heart • Pacemaker: also known as the SA (sinoatria;) node • Located in right atrium • Generates an electrical signal • Spread over both atria so they contract at the same time

2. Heart Beat continued… • Atria contract simultaneously • Signal reaches AV node • Electrical signal travels through “Bundle of His”

3. Heartbeat • Bundle of His sends signal through 2 bundles • Bundles branch and divide into fast conducting Purkinje fibers • Purkinje fibers stimulate contraction of right & left ventricles

4. Electrical Signal of the Heart • Measured using an ECG (electrocardiogram) • Called a PQRST wave

5. PQRST Wave • P: atrial excitement begins; atria CONTRACT (delay as ventricles fill) • QRS: ventricular excitement begins; bicuspid (left side) & tricuspid (right side) valves close causing “LUB” sound • T: electrical signal as ventricles recover form contraction; semi-lunar valves close causing “DUB” sound • Spacing between waves can detect heart conditions…

6. Blood Pressure • Exertion of pressure against vessel walls • Corresponds to phases of the heart beat • Ventricles contract; pressure increases • Maximum pressure during Ventricle contraction is known as SYSTOLIC Pressure

7. Blood Pressure • Ventricles relax… • Pressure drops and at lowest pressure before contraction again… • Known as DIASTOLIC pressure

8. Sphygomanometer • Reads Systolic over Diastolic • Normal Reading: 120/80 • Exercise increases blood pressure

9. Cardiac Output & Stroke Volume • Blood pumped through the heart is measured in mL/min • 2 factors affect cardiac output: heart rate & stroke volume • Heart Rate: # of beats per minute • Stroke Volume: amount of blood forced out of the heart

10. Cardiac Output • Cardiac Output = (heart rate) x (stroke volume) • Example: the average person has ~70mL stroke volume & 70 beats per minute • Cardiac Output: • 4900mL/min