Unequivocal evidence in favor of the concept that a ventricular diastolicvis a frontecontributes to ventricular filling has been established only in the following conditions: a. When the ventricle contains an abnormally small residual volume (rat, dog, turtle) b. When the ventricle contains a more nearly normal, residual volume due to ejection against the resistance of a fluid column (dog, turtle). The quantitative contribution of the ventricularvis a fronteto ventricular filling at various residual volumes and various levels of cardiac activity is still unknown. The physiological significance of diastolic suction for the return flow of blood can therefore not yet he evaluated.