When it comes to a heart attack, the difference between life and death may hinge on timing, according to the Mayo Clinic.
Researchers found a 5 percent higher chance of death - almost 2,000 more deaths a year - within 30 days of the heart attack if a person arrived at the hospital at night or on the weekend.
The Mayo Clinic examined the records 2 million heart attack patients from 42 studies.
What made the difference: The time it took from entering the hospital's door to having a balloon procedure - in which a balloon is threaded into a blood vessel and inflated to restore flow in a clogged artery.
Researchers found that during "off hours" - described as late night, early morning and weekends - patients overall experienced close to a 15-minute longer wait to get the procedure than those who went to the ER during what's considered regular business hours.
The doctors who worked on the Mayo Clinic report said a fix might be as simple as staffing.
"There are fewer staff and resources at night and on weekends - that's true," said Dr. Atsushi Sorita, the study's lead author.
Of course, experts say, a person cannot choose when to have a heart attack, but they said the important factor in any heart attack is speed of treatment.
No matter when a person suspects a heart attack, cardiologists said not to wait and to call 911. They said to get to the hospital fast and in the meantime, chew an aspirin.
ABC News' Ann Reynolds contributed to this story.