At Fighter 3, when you are reduced to 0 HP or lower, make both a Strength and a Constitution check. If you succeed at either regain 10 hit points. If you succeed at both, regain 20. You may use this extraordinary ability a number of times per long rest equal to your Strength modifier, or once — whichever is greater. If you do not succeed at either check, then you'll need to Defy Death.