Problem stacking ADS1292r ECG shield and Wifi shield on Arduino Uno
As a generic answer to these sorts of problems (same pin needed by different libraries), I have had success with slightly bending the pin of the top shield to the side to that it doesn't make direct contact with the board underneath (ie doesn't plug into the header socket).

Assuming the shields are all stackable, you can run a jumper wire from the top of the pin to any other pin which is permitted by the configuration. If not, you may have to solder a wire.

In your example, put the WiFi shield on top with its D4 pin bent to the side (with ECG shield between Uno and WiFi shield) , and run a jumper between the tops of D3 and D4 (ie on the WiFi Shield). Thus the SD Card select would now be set to D3 instead of D4, and no other connection is made to D4 on the WiFi shield.

I can't verify that you won't have trouble with other pins (eg it looks like both shields use D7).