Dr. Jessica Mega, Verily's chief medical officer

Big Silicon Valley companies have often competed for talent with specialized skills, like expertise in artificial intelligence or trendy new programming languages. Now they're competing for heart doctors. Apple hired Dr. Alexis Beatty, a cardiologist, to its growing health team in July, according to a LinkedIn search. Amazon hired Dr. Maulik Majmudar, also a cardiologist, the following month. Alphabet's life sciences company Verily named Dr. Jessica Mega as its chief medical officer almost three years ago. Mega, of course, is a cardiologist. This might just be a coincidence. Cardiologists tend to be well educated and hard working, and big tech companies have a track record of recruiting such people. In recent years, all of these companies have started to invest in products and devices that are targeted to millions of people who could benefit by tracking their heart health. Apple's smartwatch now includes an electrocardiogram, which can detect heart rhythm irregularities. Verily's study watch, which is designed for clinical trial research, also tracks heart rate and heart rhythm, and it's doing a lot of work in chronic disease management. Another Alphabet team, Google Fit, worked closely with the American Heart Association for its design revamp. Amazon's plans in cardiology are less clear, but the company does have a secretive research and development team that is working on a variety of health projects under the leadership of an electrical engineer — former Google X employee Babak Parviz. So the more likely explanation is that tech companies are interested in health care, and they have all come to the conclusion that cardiology should be an early (if not initial) target. Here's why.

It's a huge potential market

Heart disease is the No. 1 killer in the world, and strokes are among the leading causes of death. And that's not all that cardiologists treat. "Our scope covers other common disease such as high blood pressure, which impacts about a third of people in the U.S. — 75 million Americans — as well as lipid and cholesterol disorders," said Dr. Mo Elshazly, a cardiologist and assistant professor of medicine at Weill Cornell Medicine. Many cardiologists are also experts in nutrition and exercise science, which impacts a huge number of people who are committed to staying healthy. That's useful for the teams within the largest tech companies that are more focused on wellness and fitness applications, rather than on health and medical. Alphabet has Google Fit. Apple has a fitness group for its Apple Watch. And Amazon is looking at health and wellness applications for its Alexa voice assistant.

It's well-studied

Cardiology is among the most-studied fields in medicine, meaning there's already a lot of evidence to understand the root causes of heart disease, as well as how to prevent it. That's attractive for tech companies, which tend to base their development decisions on data. Some companies are also interested in running studies of their own to learn more about cardiovascular disease, which their on-staff cardiologists could support. Alphabet's Verily is funding longitudinal research, called Project Baseline, to understand why healthy people get sick, and Apple is working with Stanford University on a study to use its Apple Watch to detect heart rhythm irregularities in a diverse population.

Their consumer products are already making a difference

Let's take Apple, as an example. The company launched its first Apple Watch model with a heart rate sensor, never expecting that people would use it to discover they were pregnant, at risk for a heart attack or experiencing a dangerous irregular heart rhythm. But as people began sharing examples of how the Apple Watch saved their life, the company started to invest heavily in the science and technology to drive more of these stories. A lot of that work culminated in the first-ever clearance for a heart rhythm sensor called an ECG for Apple Watch earlier in the summer. As Apple Chief Operating Officer Jeff Williams recently explained, the journey into health was an organic one that just made sense. And heart health, given its sheer importance, seemed like the right place to start. "We didn't wake up one day and say, 'Well we've done the phone, we've done the iPad, why don't we knock out health next?'" he told CNBC. "Quite honestly, we've been really surprised with the deluge of letters and emails we've gotten where just the simple heart rate monitor was able to have such an impact on people's lives. And we've been really inspired and we want to do even more."