Right lateral thoracic radiograph of a clinically normal guinea pig illustrating measurements for the evaluation of cardiac size (60 kV, 200 mA, 20 mS, 4 mAs). CVC: maximal width of the caudal vena cava; LA: apicobasilar length of the heart; SA: width of the heart at its widest point perpendicular to LA; T4: fourth thoracic vertebra. T5: length of the fifth thoracic vertebral body; The LA and SA dimensions have been transposed onto the vertebral column starting from the cranial edge of the body of T4, calculated in units of vertebral length, and added to yield the VHS