Both of the previous responses to your post provide good advice. Care should always be used when any electricity gets near the heart. The heart operates off of very small electrical signals. A regular zapper can generate a signal that is 9000 times as strong which can disrupt the heart's operation.
Also, consider what might happen if you kill a parasite inside of the heart, or within the heart muscle by any means. The parasite would decompose where it died, possibly causing an infection, heart damage from toxins, or even blood clots.
Zappers can be a great resource but thoughtful consideration should be given to all possible consequences.