Your dog can be spayed in about two to four weeks after the heat has ended. A heat cycle lasts anywhere from two to three weeks, although a dog can still become pregnant for about a week after the cycle has ended. This two to four week limit is particularly important to reduce the amount of time spent in surgery, to limit the swelling of the organs involved, and to limit the amount of bleeding. A dog that is still in heat can be spayed but it's usually more expensive and riskier because the dog is already bleeding from being in heat. However, a dog can also be spayed before its first heat if the vet agrees to do so.