A new study identifies why more heart attacks happen in the morning, while the rate of older Americans being hospitalized for heart failure is skyrocketing.

Researchers at Emory University measured endothelial cells, known for protecting the heart, and the blood vessel function of 12 people. They checked six times during a 24-hour period. The results showed the protective cells were the greatest around eight at night and blood vessels were most relaxed at midnight.

On the other hand, blood vessel function was at the lowest levels in the early morning hours, leaving the body most vulnerable to a heart attack.

Meanwhile, the rate of older Americans being hospitalized for heart failure is skyrocketing, according to a new study. Researchers at Drexel University found a 131-percent increase in heart failure hospitalizations between 1980 and 2006 in patients over 65.

It presents a huge problem for the health care system, especially considering the aging U.S. Population and the fact that an estimated five million Americans are living with heart failure.