Showing High Score (local)

Hey guys, i would like to show high score value at high score text, but im getting this error.

Assets/Scripts/Score.cs(24,46): error CS0030: Cannot convert type float' to string’

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class Score : MonoBehaviour
{
	public Text scoreText;
	public Text endGame;
	public Text saniye;
	public float myTimer = 0.0f;
	public float life;


	public Text highScoreText;
	public float highScore = 0;
	string highScoreKey = "HighScore";

	void Start()
	{
		scoreText = GetComponent<Text>();
		endGame.text = "";
		saniye.text = "";
		highScore = PlayerPrefs.GetInt(highScoreKey,0);
		highScoreText.text = (string)highScore;
	}
	
	void Update()
	{

		life = healthBar.cur_health;
		if (life > 0) {
			myTimer += Time.deltaTime;
			Debug.Log("life < 0");
			scoreText.text = Mathf.Round(myTimer).ToString();
			}
		if (life < 0) {

			Debug.Log("life < 0");
			endGame.text = Mathf.Round(myTimer).ToString();
			scoreText.text = "";
			saniye.text ="Secs Alive";

			if(myTimer>highScore){
				PlayerPrefs.SetInt(highScoreKey, (int)myTimer);
				PlayerPrefs.Save();
			}


	}}
}

Have you tried highScoreText.text = highScore.ToString(); like you are doing for scoreText.text = Mathf.Round(myTimer).ToString(); ?