That's only for certain HUDs (broessel's is set up like that).

If you don't have one of them you'll need to open up tf/scripts/HudAnimations_tf

for buffed health mine looks like

event HudHealthBonusPulse
{
Animate PlayerStatusHealthBonusImage Alpha "255" Linear 0.0 0.2
Animate PlayerStatusHealthBonusImage Alpha "0" Linear 0.2 0.4

Animate PlayerStatusHealthvalue FgColor "buffed HP" linear 0.0 0.0

Animate PlayerStatusHealthvalueTargetID FgColor "TargetID buffed HP" linear 0.0 0.0 // <-----------

RunEvent HudHealthBonusPulseLoop 0.4
}

dying should be right under

event HudHealthDyingPulse
{
Animate PlayerStatusHealthBonusImage Alpha "255" Linear 0.0 0.075
Animate PlayerStatusHealthBonusImage Alpha "0" Linear 0.125 0.075

Animate PlayerStatusHealthvalue FgColor "low HP" linear 0.0 0.0

Animate PlayerStatusHealthvalueTargetID FgColor "TargetID low HP" linear 0.0 0.0 // <-----------

RunEvent HudHealthDyingPulseLoop 0.25
}

you can either keep the text and put what above said in ClientScheme, or use actual values there