Cardiac Cycle Timing Explained

The cardiac cycle refers to the complete sequence of events that occurs during one heartbeat. It involves the coordinated contraction (systole) and relaxation (diastole) of the heart chambers (atria and ventricles) to pump blood throughout the body.

Understanding Cardiac Cycle Phases

Each cardiac cycle is fundamentally divided into two main periods:

• Systole: This is the phase where the heart muscle contracts, pushing blood out of the heart chambers. Ventricular systole is the contraction of the ventricles.
• Diastole: This is the phase where the heart muscle relaxes after contraction, allowing the chambers to fill with blood. Ventricular diastole is the relaxation of the ventricles.

Determining Cardiac Cycle Duration

The duration of one cardiac cycle is inversely related to the heart rate. Heart rate is typically measured in beats per minute (bpm).

The formula to calculate the duration of a single cardiac cycle is:

$$ \text{Duration of Cardiac Cycle (seconds)} = \frac{60 \text{ seconds}}{ \text{Heart Rate (bpm)}} $$

For example, if a person has a resting heart rate of 75 bpm, the duration of one cardiac cycle can be calculated as:

$$ \text{Duration} = \frac{60}{75} = 0.8 \text{ seconds} $$

Therefore, a typical resting heart rate results in a cardiac cycle duration of approximately 0.8 seconds. This value represents the time taken for the heart to complete one full cycle of pumping blood.

Analysis of Options

Considering the calculation above, the duration of one cardiac cycle is typically 0.8 seconds. The options provided are:

• 0.12 seconds
• 0.57 seconds
• 0.9 seconds
• 0.8 seconds

Based on standard physiological measurements and calculations, 0.8 seconds is the most accurate representation of the duration for one complete cardiac cycle at a normal resting heart rate.