It's a group of conditions related to your heart. Some are problems with the muscle itself, the valves, or how it beats, including cardiomyopathy, atrial fibrillation, and heart failure. Others affect your blood vessels, like hardened arteries and strokes. Unhealthy foods, lack of exercise, and smoking are often what lead to heart disease. So can high blood pressure, infections, and birth defects. But other things might surprise you.