The relationship among cardiac output, stroke volume, and heart rate is quite direct.
Cardiac Output = Stroke Volume X Heart Rate
Stroke Volume = End Diastolic Volume - End Systolic Volume
Although the concept applies to either ventricle, usually stroke volume measurements are made on the left ventricle, which has the larger workload.
The Frank-Starling Law states that the larger the preload, or volume of blood entering the heart during diastole (relaxation) the greater the volume ejected during the subsequent systole, or contraction. This happens because a greater volume of blood entering the heart causes stretching of the cardiac muscle, which in turn causes a larger number of actin/myosin cross bridges to form, increasing the power of the heart beat that follows.
Elevated afterload, which is resistance in the aorta, causes reductions in stroke volume. This is uncommon in healthy hearts, but can be seen in individuals with hypertension and/or aortic blockages.