Cardio is definitely a must, it helps build up your heart like Agraham said. You can see all of these super strong bodybuilders in the gym but their cardio is horrible, it makes me worry about their heart health. I try to do cardio at least 3 days a week just to help my heart strength. HIIT training really helps out! But I think a mix of eating right, resistance training, and cardio training will lead to a healthy life.