Keep repeating message at certain rate.

Im trying to make a healing zone for my player and this is what i got so far:

		void OnTriggerEnter(Collider entity){
		if(entity.CompareTag("Friendly")){
			entity.SendMessage("Heal", new HealthEvent(gameObject, 1), SendMessageOptions.DontRequireReceiver);

		}
	}

Works pretty well so far except i need the message to repeat at a certain rate (variable) as long as the friendly entity is inside the collider.