Live by Them: Mishneh Torah Hilchot Shabat 2:

It is permitted to violate the sabbath in order to save a life. Maimonides, himself a physician, has a lovely comment on this.

It is forbidden to hesitate before transgressing the Sabbath [laws] on behalf of a person who is dangerously ill, as is reflected in Leviticus 18:5,] "[The laws] which a person shall perform to live through them; " one must live through them, and not die because of them. This teaches that the judgments of the Torah are only sustained through mercy, kindness, and peace in the world.