This goes on an object maybe?

DamageOnCollision

using UnityEngine;
using System.Collections;

public class DamageOnCollision : MonoBehaviour {
 
   public int damagePerHit = 1; 
	public bool destroyOnCollision = true;
	public float destroyDelay = 0.1f; 
	 
	void OnCollisionEnter(Collision col){ 
		var heart = col.collider.GetComponent<Heart>();
		if(heart != null){
			heart.DoDamage(damagePerHit, col);
		}
	
		if(destroyOnCollision)
			Destroy(gameObject, destroyDelay);
	}
	
	// if this thing is a trigger 
	void OnTriggerEnter(Collider col){ 
		var heart = col.collider.GetComponent<Heart>();
		if(heart != null){
			heart.DoDamage(damagePerHit, col);
		}
		
		if(destroyOnCollision)
			Destroy(gameObject, destroyDelay); 
	}
	
	// if this thing is a charactercontroller 
	void OnControllerColliderHit(ControllerColliderHit hit){ 
		var heart = hit.collider.GetComponent<Heart>();
		if(heart != null){
			heart.DoDamage(damagePerHit, hit);
		}
		
		if(destroyOnCollision)
				Destroy(gameObject, destroyDelay); 
	}
}