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Ventricular Systole

Systole ventriculorum

For medical students2 min readUpdated 2026-10-10

Ventricular systole is a critical stage of the cardiac cycle during fontstyle the myocardium contracts, increasing intraventricular pressure and ensuring the ejection of blood into the great vessels. The entire process is strictly divided into the periods of tension (contraction) and ejection, each comprising specific phases with unique hemodynamics.

First heart sound ($S_1$)Occurs due to myocardial tension and closure of the atrioventricular valves.
Isovolumetric phaseLasts 30 ms; the chamber volume remains unchanged during this moment.
Aortic pressureIncreases from 80 to 120 mmHg during the rapid ejection phase.
Phase transitionDetermined by changes in pressure, volume, and valve status.

Chronostructure of the Cycle and Phase Criteria

The overall work of the ventricles is divided into 9 sequential phases. The starting point of the entire cardiac cycle is considered to be ventricular presystole, which temporally coincides with atrial systole and lasts 100 ms.

The transition of the heart from one phase to another is accompanied by intermediate events. The shift between stages is always characterized by changes in three key hemodynamic parameters:

Ventricular systole itself is globally divided into two periods: tension (contraction) and ejection.

Period of Myocardial Tension

This period prepares the heart chambers for the subsequent ejection of blood. Intraventricular pressure begins to rise rapidly. The period includes two phases:

  1. Phase of asynchronous contraction. Lasts 50 ms in the left ventricle and 70 ms in the right. Contraction of myocardial fibers begins unevenly due to differences in the arrival time of excitation. The impulse sweeps through the tissues sequentially: first the areas near the Purkinje fiber terminals, then the papillary muscles, the interventricular septum, and the apex. Contracting areas stretch neighboring zones, so the overall length of the ventricles and their volume do not change. Atrial pressure drops, and the leaflets of the atrioventricular valves passively float upward.
  2. Phase of isometric (isovolemic) contraction. Lasts 30 ms. Excitation synchronously encompasses all cardiomyocytes. It begins when the backflow of blood snaps the atrioventricular valves shut. The semilunar valves are still closed because the pressure is not yet sufficient to open them. The ventricle becomes completely sealed, pressure inside it rises sharply, while volume remains unchanged.

Note: It is during this period that the first heart sound ($S_1$) is formed. It is caused by the vibration of the snapped shut atrioventricular valves, as well as the tension of the chordae tendineae and the muscular wall.

Period of Blood Ejection

When intraventricular pressure begins to exceed the diastolic pressure in the vessels (aorta and pulmonary trunk), the blood flow opens the semilunar valves. The atrioventricular valves remain tightly closed. The ejection process begins, which is divided into two phases:

  1. Phase of rapid ejection. Lasts 120 ms for the left ventricle and 110 ms for the right ventricle. The main volume of blood is ejected during this time. Since the inflow of blood from the heart into the vessels significantly exceeds its outflow into capillaries, pressure in the major arteries rises sharply: in the pulmonary trunk from 15 to 30 mmHg, and in the aorta from 80 to 120 mmHg. The phase ends at the moment of peak pressure in these vessels.
  2. Phase of reduced (slow) ejection. Starts when ventricular pressure reaches its maximum, and lasts 130 ms for both halves of the heart. The outflow of blood from the aorta and pulmonary trunk to the periphery begins to exceed its input from the heart, causing vascular pressure to gradually decrease.

Throughout both ejection phases, the pressure gradient is maintained: intraventricular pressure strictly exceeds the pressure in the great vessels. This is an obligatory physical condition for the continued ejection of blood.

Mnemonic

To remember the sequence of myocardial region contraction during the asynchronous contraction phase, use the mnemonic PPVA: Purkinje fibers → Papillary muscles → Ventricular septum → Apex.

Frequently asked questions

What values (in mmHg) does the pressure in the left and right ventricles reach at the end of the tension period?

At the end of the tension period, intraventricular pressure rises to the values necessary to open the semilunar valves. In the left ventricle, pressure reaches 75–85 mmHg, as it must exceed aortic pressure. In the right ventricle, pressure rises to 15–20 mmHg, which is slightly higher than the pressure in the pulmonary trunk. Immediately after reaching these values, the semilunar valves open, the tension period ends, and the period of blood ejection into the great vessels begins.

What is the total duration of ventricular systole in a resting human?

The total duration of ventricular systole is 0.33 s (or 330 ms). This time is composed of the sequentially occurring contraction phases:

  • Asynchronous contraction — 50 ms.
  • Isometric contraction — 30 ms.
  • Rapid blood ejection — 120 ms.
  • Slow blood ejection — 130 ms.

The first two phases form the tension period, and the subsequent two form the ejection period. Ventricular systole begins after atrial systole and ends when the myocardium transitions to relaxation.

What volume of blood (in milliliters) is normally ejected by the ventricle during the ejection period?

During the ejection period, a ventricle normally ejects 65 ml of blood. This parameter represents the stroke volume (ejection volume) that the heart chamber pumps out in a single contraction. Exactly the same volume of blood is ejected from the left ventricle into the aorta and from the right ventricle into the pulmonary trunk. The stroke volume is calculated as the difference between the end-diastolic volume of 125 ml and the end-systolic volume of 60 ml remaining in the chamber after systole.

Why does ventricular volume not change during isometric contraction?

During this phase, both the atrioventricular and semilunar valves are completely closed. The heart chamber turns into a closed, sealed cavity. The muscles contract, increasing pressure, but blood cannot leave the ventricle, so the volume remains constant.

What causes the formation of the first heart sound?

The first (systolic) heart sound is formed during the tension period. The main cause of its occurrence is the vibration of the tightly closing atrioventricular valves, as well as the strong tension of the chordae tendineae and the contracting myocardium.

What serves as a signal for the end of the slow ejection phase?

The slow ejection phase ends at the moment when ventricular cardiomyocytes cease active contraction and begin transitioning into relaxation (diastole).

How do the semilunar valves open?

They open exclusively due to the pressure gradient: as soon as the rising ventricular pressure becomes higher than the diastolic pressure in the aorta and pulmonary trunk, the blood flow mechanically pushes the valve cusps apart.

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