The Cardiac Cycle
Def: The cardiac events that occur
from beginning of one heart beat to the beginning of the next.
1
Beat = 0.8 sec
Systole
= 0.3 sec
Diastole
= 0.5 sec
•
Heart at rest
–
Blood flows from large veins into atria
–
Passive flow from atria into ventricles
•
Atria (R & L) contract simultaneously
–
Blood forced into ventricles
•
Ventricles (R & L) contract simultaneously
–
Atrioventricular valves close à “lubb” sound
–
Blood forced into large arteries
•
Ventricles relax
–
Semilunar valves close à “dub”
Regulation of Heart Rate
Electrolytes
Na+,
K+
Ca+
Hormonal
regulation
Epinephrine
Thyroxine
Other
factors
Gender,
age, size, health, physical fitness
