In over a decade as a cardiologist, Dr. Tara Narula has seen a major risk factor for heart disease in 90% of her patients. It's completely preventable — but we're not talking about it enough. "My patients are walking around with this level of chronic stress that is unimaginable," she told Business Insider. "And most of my patients don't know how damaging it can be." Chronic stress can be a silent killer, putting strain on your heart that can prompt serious or even life-threatening conditions