The term systole means to contract, and diastole means to relax. Atrial systole is contraction of the atrial myocardium, and atrial diastole is relaxation of the atrial myocardium. Similarly, ventricular systole is contraction of the ventricular myocardium, and ventricular diastole is relaxation of the ventricular myocardium. When the words "systole" and "diastole" are used without reference to specific chambers, however, they mean ventricular systole or diastole.
