No your heart does not completely stop when you sneeze because if your heart actually did stop when you sneeze then you would die or at least become unconscious until it starts back up.
Your heartbeat however does slow down when you sneeze and the blood flow slows down but after you sneeze your heart speeds back up to normal and the blood flow is normal again as well.
The intrathoracic pressure in your body momentarily increases which causes a decrease of blood flow back to your heart.
The electrical activity of your heart stays the same though so the heart always remains pumping although a bit slower.
It would be a bad thing if our hearts did stop even for a moment when he sneezed because the heart is very important to keeping us alive.