Purpose Detrusor nonvoiding contractions occur in up to 70% of healthy individuals. These contractions increase in those with pathological detrusor function and may be associated with afferent activity. We examined nonvoiding contractions in the urethane anesthetized guinea pig bladder and studied the effect of filling rate and intravesical volume. Materials and Methods A total of 14 guinea pigs were anesthetized and underwent bladder catheterization at the dome. In 6 guinea pigs bladder infusion was continuous and 2 physiological filling rates were used, including 25 (0.75 HD) and 50 μl per minute (1.5 HD). In another 8 guinea pigs isovolumetric cystometry was done by filling the bladder incrementally and recording at low, medium and high intravesical volume. Results Nonvoiding contractions were apparent in all animals. Contractions increased in frequency and amplitude as the bladder filled. Different phases were identified. Immediately after a void no nonvoiding contractions were observed, followed by continuous activity, first with small contractions, and later with small and large contractions. Small nonvoiding contractions showed a phasic pattern in frequency while the frequency of large nonvoiding contractions slowly increased or remained stable. The frequency and amplitude of nonvoiding contractions were higher at a faster filling rate and a higher intravesical volume. Conclusions Nonvoiding contractions are present in the anesthetized guinea pig. Under normal physiological conditions they increase in amplitude and frequency with the increase in the filling rate and in intravesical volume. Small and large nonvoiding contractions differ in frequency pattern and occur at different bladder filling periods. This may illustrate different afferents functioning during bladder filling, which could be important for understanding bladder pathology.