Final answer:
The left ventricle has the thickest myocardium due to the greater pressure it must generate to overcome resistance in the systemic circuit.
Step-by-step explanation:
The left ventricle has the thickest myocardium. The ventricles are the primary pumping chambers of the heart, and the left ventricle must generate a much greater pressure to overcome greater resistance in the systemic circuit. Therefore, it has a thicker muscular layer compared to the right ventricle.