How Does the Heart Start Beating? This Is What the First Heartbeat Looks Like

How do heart cells go from complete silence to beating? People attach so much importance to the heartbeat that this phenomenon has been a central point in many investigations over the years. However, the details of the first heartbeat remain a mystery to most. Fortunately, a pair of scientists from Harvard University have discovered one of the keys to understanding, in greater depth, how the heart works.

By observing zebrafish embryos during a key point in their development, it has been possible to examine the cardiac process in real time. What is curious is that initially the team was not looking to analyze this, but rather to obtain images of the electrical activity of cells in developing zebrafish and how they learn to communicate and cooperate with each other. 

So what we present here is nothing more than another accidental discovery — but an extremely important one for the scientific community. 

Details of the First Heartbeat

The first heartbeat is an event that happens only once in a lifetime, though it is not obvious from the outside. We only perceive the synchronized vibration of all cardiac cells once this organ begins to function. The steps prior to beating can only be observed using microscopes and bright fluorescent proteins, which is why the Harvard team had to resort to this method with zebrafish. 

When studying them, they noticed that as a vertebrate embryo grows, the tissue of its heart begins to beat long before it is needed. But what is most curious is that all the cells of the heart suddenly begin to beat all at once, forming a synchronized movement. That would be our first heartbeat. 

These results suggest that, after all, cardiac tissue functions like a switch: one moment it is off and the next it vibrates following an established pattern.

However, certain details caught the scientists’ attention. In developing zebrafish hearts, each cell starts to beat on its own and, unlike an adult heart, the beats are not coordinated by specialized cells. The findings show that heart cells begin to beat suddenly and simultaneously as calcium levels and electrical signals increase. Furthermore, each heart cell has the ability to beat on its own.

Heartbeats were discovered in different locations in different zebrafish, suggesting that there is nothing special about the cells that activate first. Since the heart cells start beating instantaneously, they must develop the ability to beat and sense the beats of their neighbors before the first heartbeat. 

So everything seems to indicate that becoming a complete organism from a handful of cells, with functional tissues and organs, is a complicated process that begins automatically. Although it is synchronized, it requires cells to organize precisely and begin working together in that first beat.

New Findings About the Human Heart?

The zebrafish embryo offers a unique opportunity to study the heart because it is transparent, grows in just 24 hours, and numerous images of it can be taken underwater. That is why scientists at Harvard believe it could help us understand cardiac development in other vertebrates, including humans.

“The heart beats around 3 billion times in a human lifetime, and it must never take a break. We wanted to see how this incredible machine is turned on for the very first time.”

Adam Cohen, researcher at Harvard University

Furthermore, learning about the mechanisms behind heartbeats is fundamental to understanding what happens in situations where the cardiac tissue regulating this phenomenon does not develop properly or begins to malfunction. Therefore, this study of the basic biology of heartbeats could help scientists understand heart rhythm disorders in human beings. 

But we cannot draw hasty conclusions. Despite millennia of research into the developing heart — dating back to Aristotle’s observations on chicks — the details of how human cells begin to beat are still a mystery. 

All we have seen here is the first beat of a vertebrate heart, which may or may not be similar to our own. 

References:

The very first beat: how a heart starts to pulse