SYSTOLE AND DIASTOLE

in prosody, systole is the shortening of a syllable that is by pronunciation or by position long. Systole is most often used to adjust the rhythm of a line to achieve metrical regularity. The word is from the Greek systole, meaning, literally, contraction. Diastole, the opposite of systole, is the lengthening of a short quantity or syllable for metric irregularity. The word is from the Greek diastole, meaning the act of expanding or dilating.