Which lasts longer in the cardiac cycle?

Which lasts longer in the cardiac cycle?

• A. Diastole
• B. Systole
• C. Both are equal
• D. Neither lasts

Answer: (A)

The main concept here is the relative duration of the two phases of the cardiac cycle. Diastole lasts longer than systole at normal resting heart rates because the heart spends more time relaxing and filling with blood than contracting and ejecting it. During diastole the ventricles relax, the AV valves open, and blood flows in from the atria, with a portion of filling occurring passively and a final atrial kick helping to top off the volume. Systole, the contraction phase, must quickly generate enough pressure to eject blood into the great vessels, so it is the shorter portion of the cycle. An example at rest is diastole about 0.5 seconds and systole about 0.3 seconds, making diastole the longer phase overall. While increasing heart rate shortens diastole more than systole, diastole remains longer at typical resting rates, so the correct statement is that diastole lasts longer.

The main concept here is the relative duration of the two phases of the cardiac cycle. Diastole lasts longer than systole at normal resting heart rates because the heart spends more time relaxing and filling with blood than contracting and ejecting it. During diastole the ventricles relax, the AV valves open, and blood flows in from the atria, with a portion of filling occurring passively and a final atrial kick helping to top off the volume. Systole, the contraction phase, must quickly generate enough pressure to eject blood into the great vessels, so it is the shorter portion of the cycle. An example at rest is diastole about 0.5 seconds and systole about 0.3 seconds, making diastole the longer phase overall. While increasing heart rate shortens diastole more than systole, diastole remains longer at typical resting rates, so the correct statement is that diastole lasts longer.