Systole – The Cardiac Cycle (Systole and Diastole)

In a healthy heart, medicine distinguishes between two heart sounds:

1. When the ventricles contract during the heartbeat phase (systole).
2. The second heart sound occurs at the end of the systole, when the mitral and tricuspid valves close (diastole).

When the heart is diseased, doctors refer to heart murmurs. Heart murmurs occur when the heart valves no longer open or close properly. They can be heard when listening with a stethoscope. This allows doctors to determine whether the heart valves and the heart are healthy and functioning optimally.

The Anatomy of the Heart © designua | AdobeStock

Through its rhythmic muscle contractions, the heart generates pressure that pumps blood into the circulatory system. This pressure inside the blood vessels is called blood pressure. A certain level of pressure is necessary to ensure that all vessels are supplied with blood.

To determine blood pressure, two values are required:

• The diastolic and
• systolic blood pressure.

The systolic pressure is the higher of the two readings. It indicates the maximum pressure developed in the left ventricle during the contraction and ejection phases. This contraction and ejection phase is called systole. In a healthy person, systolic pressure ranges between 110 and 130 mmHg.

Diastolic blood pressure is the lower reading. It corresponds to the lowest pressure during the relaxation and expansion phase of the heart muscle. The period between the greatest drop in pressure—diastolic pressure—and the greatest increase in pressure—systolic pressure—is medically referred to as diastole. The heart chambers fill with fresh blood during diastole. In a healthy person, diastolic pressure ranges between 80 and 89 mmHg.

In general, blood pressure varies from person to person. It also depends on the situation and anatomy, such as

• the elasticity of the blood vessels,
• the heart’s pumping and pressure output—that is, the strength of its contractions. During physical exertion, the organs require more blood than when at rest. For this reason, an increase in blood pressure and heart rate is necessary.
• the diameter of the blood vessels and the associated resistance. The greater the resistance to blood flow, the higher the pressure must be.
• body position, as well as
• signals from certain nerves and hormones.

A blood pressure reading of up to 120/80 mmHg is considered optimal at rest. Readings not exceeding 129/84 mmHg are considered normal. A blood pressure of up to 139/89 mmHg is considered high normal.

• Mildly elevated blood pressure: readings between 140 and 159 over 90 and 99 mmHg
• Moderately elevated blood pressure: readings between 160 and 179 over 100 to 109 mmHg
• Severe hypertension: Readings of more than 180/110 mmHg

Blood pressure can be measured using digital or analog blood pressure monitors © Photo Sesaon | AdobeStock

If blood pressure deviates more or less significantly from normal values, an examination of the heart is necessary. This is done, among other methods, with an electrocardiogram (ECG).

In addition, the doctor may fit the patient with a continuous blood pressure cuff (long-term ECG). It measures the patient’s blood pressure over a 24-hour period. This helps determine whether blood pressure is consistently too high or too low, or whether these are isolated incidents.

Systole and diastole together form the central cycle of cardiac activity and ensure a continuous flow of blood. During the contraction phase—that is, systole—blood is pumped into the systemic circulation, while during the relaxation phase, the heart can fill with blood again. The contraction phase of the heart muscle is divided into the tension phase and the ejection phase, during which the semilunar valves are closed and the mitral and tricuspid valves are open.

During this phase, blood is pumped into the systemic circulation and into the lungs, primarily via the pulmonary artery and the aorta. The heart rate determines the duration of a heartbeat and influences the overall workload on the heart muscle. At the end of the systole, the second heart sound occurs as the valves close.

The semilunar valves open again during the filling phase, allowing the accumulated blood to flow into the ventricle. A smooth process is crucial; otherwise, heart murmurs or functional disorders may occur. If the heart becomes diseased or the heart valves no longer close properly, blood flow can be disrupted.

Overall, it is clear that systole and diastole form a perfectly coordinated system that is essential for supplying the body with blood.

What is systole?

Systole is the contraction phase of the heart. During this phase, the heart muscle contracts and blood is pumped out of the heart chambers.

What happens during diastole?

Diastole is the relaxation phase during which the ventricles fill with blood. During this phase, the semilunar valves open, allowing blood to flow from the atrium into the ventricle.

How are systole and diastole related?

Systole and diastole together form the cardiac cycle. During systole, blood is ejected, while diastole refills the heart.

What role do the heart valves play?

During systole, the semilunar valves are open and the mitral and tricuspid valves are closed. This prevents blood from flowing backward.

How can you detect heart function disorders?

Abnormalities can be detected through an ECG or by listening with a stethoscope. Heart murmurs may indicate problems with the heart valves.