Although the walls of the left ventricle are thicker than those of the right ventricle, the volume of the ventricles is the same. Why is this necessary?
The left ventricle of the human heart is larger (weighs more) than the right. This is because it has the thicker wall, and therefore greater muscle mass.
Both ventricles contract in unison, not exactly at the same precise moment in the cardiac cycle, but in synchrony, such that for every contraction of the left ventricle there is a contraction of the right. In the healthy heart, both chambers empty almost completely with each contraction.
The left ventricle is thicker and more muscular because its contraction must pump blood at high pressure throughout the entire body.
The right ventricle is not so strong, and plumps against a lower pressure, having only to pump blood through the lungs.
The volumes of the right and left ventricular chambers are roughly equal. The stroke volume (number of milliliters of blood pumped with each contraction) is equal for both sides of the heart (right and left ventricles). If this were not the case, there would be a disparity in the volume of blood returning from the lungs compared to the volume returning from the rest of the body. Similarly, there would be a difference in the output (milliliters per minute) from the right versus left ventricles. The imbalance would be catastrophic as pressures would go awry and the heart would quickly fail. The pulmonary (lungs) circulatory system and the systemic (remainder of body) circulatory systems are connected in series as an overall single, closed system. The volume of blood plumped in one minute by the left ventricle must equal that pumped by the right.
The references illustrate the anatomy of the human heart. The second reference also includes information on common heart diseases.
The walls of the left ventricle is thicker than the right because the right ventricle only pumps blood to the lungs. The left ventricle has to pump blood all around the body!! That's a long way to go for blood and it needs an "extra" push by the stronger walls. Hope this helps you:))