BSCI 202 Heart and Vessels Note

Heart and Vessels


Phases of the Cardiac Cycle
● 1. Ventricular filling
○ AV valves are open; pressure low
○ 80% of blood passively flows into ventricles
○ Atrial systole occurs, delivering remaining 20%
○ End diastolic volume (EDV): volume of blood in each ventricle at end of
ventricular diastole
● 2. Ventricular systole
○ Atrial diastole; ventricles begin to contract
○ Isovolumetric concentration phase (closed valves)
○ Ventricular pressure > artery pressure
○ End systolic volume (ESV): volume of blood remaining in each ventricle after
systole
● 3. Isovolumetric relaxation
○ Ventricles relax; atria relaxed and filling
○ Blood closes SL valves
○ AV valves open; cycle begins again at step 1

Cardiac Output (CO)
● Volume of blood pumped by each ventricle in one minute
● CO = heart rate (HR) x stroke volume (SV)
○ HR = number of beats per minute
○ SV = volume of blood pumped by one ventricle with each beat
● Normal - 5.25 L/min
○ CO (ml/min) = HR (75 beats/min) x SV (70 ml/beat)
○ = 5.25 L/min


Cardiac Output (CO) Variation
● CO increases if either/both SV or HR increased
● Maximal CO is 4-5 times resting CO (~25 L/min)
○ Up to 35 L/min in trained athletes
● Cardiac reserve - difference between resting and maximal CO


Regulation of Stroke Volume
● SV = EDV - ESV
○ EDV - length of ventricular diastole and venous pressure