Abstract: Apparatus and methods to inject fluids downhole, such as: a sample chamber configured to provide a fluid in a wellbore extending into a subterranean formation; a flow line configured to be fluidly coupled to the subterranean formation; a piston disposed in and separating the sample chamber into first and second chambers; a first fluid port fluidly coupling the first chamber to the flow line; a second fluid port fluidly coupling the second chamber to a fluid source having a pressure greater than the pressure in the first chamber; and a flow regulator fluidly coupled to the first or second fluid port, and configured to regulate the flow of the fluid provided in the sample chamber into the formation.