The right ventricular end-diastolic diameter of the heart is the internal diameter of the right ventricle at the end of diastole. The normal human heart is divided into four chambers; the upper part is two atria, divided by the interventricular septum into right and left atria, and the lower part is two ventricles, divided by the interventricular septum into right and left ventricles. The heart has a cardiac cycle from the beginning of one beat to the beginning of the next, which is divided into diastolic and systolic phases. The right ventricular end-diastolic diameter of the heart refers to the inner diameter of the right ventricle at the end of the diastolic phase of the heart during the cardiac cycle. Its enlargement suggests that organic heart disease may be present. Those with an abnormal right ventricular end-diastolic diameter need to look for possible diseases under the guidance of a doctor and treat them promptly to avoid delays.