zViagra works by mimicking nitric oxide which opens blood vessels carrying blood to the penis thereby increasing blood flow to the penis and facilitating an erection. zViagra does not cause an erection by itself. Erotic stimuli are still necessary to cause the erection. z Viagra can have effects on other parts of the cardiovascular system and men with heart conditions must be careful about taking Viagra. Thus, some men cannot take Viagra. zViagra may or may not have an effect on a normal male depending on their individual  physiology. zViagra does increase blood flow in women as well leading to more vasocongestion and is being studied with regards to its effect in women.