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A substance called trimethylamine N-oxide, which is produced when your body digests red meat, may raise the risk of cardiovascular problems.

Experts used to think that red meat raised your risk of heart disease simply because it was high in saturated fat. But today that picture has gotten more complicated thanks to the discovery of a metabolite � a substance produced during digestion and metabolism � called trimethylamine N-oxide, or TMAO.

According to a news article published June 11 in JAMA, three recent analyses have linked high blood levels of TMAO with a higher risk for both cardiovascular disease and early death from any cause. In one of those studies, researchers found that people with higher levels of TMAO in their blood may have more than twice the risk of heart attack, stroke, or other serious cardiovascular problems, compared with people who have lower levels. Other studies have found links between high TMAO levels and heart failure and chronic kidney disease.

Research we're watching

If you have coronary artery disease, you may be at higher risk for cognitive problems, according to a study published in the June issue of the Journal of the American College of Cardiology. People with coronary artery disease have blockages in the arteries that lead to the heart. When blood flow to the heart is slowed or blocked, the result can be a heart attack or the chest pain known as angina.

Study authors looked to see whether this condition had any effect on thinking skills. They selected people with no history of heart disease and followed them for 12 years, administering three cognitive tests throughout the course of the study. Ultimately, 5.6% of people in the study experienced a heart attack or angina. Researchers found that these people were not more likely to have experienced cognitive decline before their heart episode or immediately after, but were at much higher risk for cognitive decline in the years that followed. It's not clear why this occurred, but the study authors say that doctors should be aware of this risk and should monitor people with coronary artery disease carefully.

The simple version of cardiopulmonary resuscitation � pushing hard and fast on the chest � can double a person's odds of surviving cardiac arrest.

If someone suddenly collapses and stops breathing, the most likely cause is cardiac arrest. An electrical malfunction causes the heart to beat rapidly and chaotically � or to stop beating altogether. But if a bystander immediately begins chest compressions, which mimic the heart's pumping action, blood keeps flowing to the person's brain.

For more than a decade, guidelines have recommended this simpler version of cardiopulmonary resuscitation (CPR), which does not involve the mouth-to-mouth breathing used in standard CPR.

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Q.ÌýAfter my heart attack, my doctor told me that damaged heart muscle cannot be replaced. If this is true, why am I walking on a treadmill five days a week? Is this helping repair the heart muscle damage or strengthen what's left of my heart muscle?

A.ÌýYour skeletal muscles can repair themselves after an injury â€� pull your calf muscle and, after a few days or so, it heals. Until recently, it was believed that the human heart didn't have this capacity. But the heart does have some ability to make new muscle and possibly repair itself. The rate of regeneration is so slow, though, that it can't fix the kind of damage caused by a heart attack. That's why the rapid healing that follows a heart attack creates scar tissue in place of working muscle tissue.

Research we're watching

Fewer older adults are having heart attacks, and more are surviving them, according to a study published March 15 in JAMA Network Open.

Researchers analyzed data from more than 4.3 million people ages 65 and older who had suffered heart attacks over a 20-year period beginning in 1995. Back then, 20% of those included in the study died from their heart attacks. By 2014, that number had fallen to 12%.

After a serious heart-related event, cardiac rehabilitation can help you feel better and live longer.

If you have a heart attack, heart surgery, or another cardiac event, what's the best way to prevent future heart problems? Participate in cardiac rehab, a program that provides supervised exercise and teaches you the fundamentals of a heart-healthy lifestyle over a three-month period.

"The benefits of cardiac rehab are indisputable. It's more effective than any other intervention for preventing future heart-related problems and hospitalizations," says Dr. Hicham Skali, associate director of the Cardiac Rehabilitation Program at Harvard-affiliated Brigham and Women's Hospital. Eligible people who participate in cardiac rehab have a 24% lower risk of dying of cardiovascular disease compared with those who do not attend a rehab program. Cardiac rehab has also been found to improve your ability to exercise and your quality of life, he adds.

Ask the doctor

Q. I just got a stent placed in my heart artery and feel great again. If it develops problems, can it be treated?

A. Stents, the tiny wire-mesh tubes used to prop open blocked arteries, are useful for treating heart attacks and chest pain that occurs with physical activity. They're placed during a coronary angioplasty and stenting procedure, which usually involves snaking a thin tube (catheter) through a vessel in the upper thigh or the wrist up to the heart. After more than two decades of use, today's stents are safer and more effective that the original versions. Problems can still arise, but they are uncommon and treatable.

Learn how to recognize and prevent this dangerous condition, known as venous thromboembolism, or VTE.

When a blood clot blocks an artery supplying the heart or the brain, the result is a heart attack or stroke. Most Americans are familiar with these two serious health threats. But they're probably less familiar with the dangers of venous thromboembolism, or VTE � a clot that forms in a vein.

A clot in the leg or arm, known as deep-vein thrombosis, can cause pain, swelling, and redness in the affected limb. But the real threat occurs if the clot breaks off and travels to the lungs, causing a pulmonary embolism.

In the journals

People who have had a heart attack or a stroke are routinely prescribed a statin to reduce the risk of a repeat event. But by also following a Mediterranean-style diet, they can improve their chance of living longer, suggests a study in the Feb. 1, 2019, issue of the International Journal of Cardiology.

The study looked at 1,180 people, average age 68, who had at least one previous heart attack or stroke, and recorded their statin use and diet intake at the study's beginning. The researchers identified the people who faithfully followed a Mediterranean-style diet. A Mediterranean-style diet involves consuming medium to high amounts of whole fruits and vegetables, whole grains, legumes and nuts, olive oil, and poultry and fish, with limited amounts of red meat, alcohol, and dairy.

Why do heart attack rates rise on Monday mornings and the week after daylight savings time begins?

Deep inside your brain is a small cluster of cells that serves as your body's master clock. These cells govern your circadian rhythm, the 24-hour internal clock that keeps your body in sync with the day-night cycle. But nearly all your cells also have their own clocks to ensure that each one performs its unique role � such as producing proteins or releasing hormones � at the right time.

These biological timekeepers are under genetic control. But what happens if our behavior or environment is out of sync with our internal clocks? Understanding the potential health consequences of that misalignment is the focus of the Medical Chronobiology Program at Harvard-affiliated Brigham and Women's Hospital, says Dr. Frank Scheer, who directs the program.