Cuban doctors receive only about 25% of what foreign governments pay Cuban authorities for their services (most host countries also provide Cubans with free accommodation, though of widely varying quality). These doctors have no way of negotiating their salary with the Cuban authorities, since they do not have the right to organize independent unions to defend their demands. In Cuba, the unions are controlled by the State and function as mere transmission belts for the policies and decisions of the Communist Party.
Doctors abroad are subject to a series of government rules that limit their mobility and try to prevent desertions. For example, they have their compensation, or part B2B Fax Database of it, deposited by the State in Cuba itself, and they must leave their spouses and/or minor children on the island. In addition, they must hand over their passports to their supervisors as soon as they arrive in the foreign country where they will work.
Desertion carries severe penalties such as Cuba for eight years despite continuing to be Cuban citizens. However, Cuban doctors are more than willing to practice abroad under the sponsorship of their government. In addition to the humanitarian feelings that may motivate them, the very small 25% payment they receive for their services is much better than what they would normally earn in Cuba.