Disclosed are subsurface safety valves having multiple pistons used to increase the opening force. One safety valve includes a housing having a piston bore defined therein and configured to receive hydraulic fluid pressure, the piston bore providing an upper bore having a first diameter and a lower bore having a second diameter smaller than the first diameter, a piston assembly movably arranged within the piston bore and comprising an upper piston arranged in and configured to sealingly engage the upper bore and a lower piston arranged in and configured to sealingly engage the lower bore, and a connecting rod coupling the upper and lower pistons, wherein a cavity is defined between the upper and lower pistons within the piston bore and the piston rod extends within the cavity.