cardiac cycle

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