context: If you've felt a rapidly beating heart out of the blue, you might have checked into it and come across the term âsupraventricular tachycardia,â or SVT. Most of the time, it doesn't cause any serious health problems, though it's natural that a really fast heartbeat would concern you. Be sure to make an appointment with your doctor if you've felt your heart racing when you haven't been exercising or feeling anxious. When it comes to SVT, there's no one-size-fits-all answer. It's actually a group of several different heart conditions that have a few things in common. But before you get into all the types of SVT, you first need to know what happens when your heart pumps the right way. Your heart has four chambers: the left and right atria, on the top, and left and right ventricles, on the bottom. To pump blood, each chamber has to squeeze in and out at just the right moment. To time all of this just right, your heart has what's sometimes called a ânatural pacemaker,â a cluster of cells that sends little electrical impulses to each chamber. Its formal name is the sinoatrial node. You may hear your doctor called it the SA node for short. Each time this SA node contracts, it sends a signal across to your left atrium and a separate one down toward your ventricles. A second cell clump, the atrioventricular ( AV) node, helps move that message. If the signals travel along the way they should, your heart beats at its normal rate. But sometimes those signals don't move the way they should. That's where SVT might come in. The term has Latin roots. Supraventricular means âabove the ventricles,â which are the lower two sections of your heart. Tachycardia means âfast heart rate.â Rapid heart rates can start in various places of a heart. For you to get a diagnosis of SVT, your problem must start in the atria, the upper two chambers. Once your doctor has narrowed that down, then he can start to figure which type you have. This is the most common kind. You may also hear it called â AV nodal reentrant tachycardia,â or AVNRT for short. If you have this type, the cells near your AV node don't send electrical impulses through your heart correctly. The cells create a circular signal around the node instead of simply passing them along as they should. The signal, which spurs each chamber of your heart to beat, is moving in a small circle like a car around a race track. That is what causes the extra beats. Like AVNRT above, this happens when cells in your heart are sending electrical impulses in an extra circle. Normally, each signal your SA node sends out stops once it travels through all the chambers and causes a single heartbeat. This node must start a new electrical pulse to get the next heartbeat going. But with this kind of tachycardia, the signal loops back to the AV node after it's traveled through the ventricles instead of moving along as it should. That's what ends up causing the extra heartbeats. Normally, the SA node is the only place that can create a new electrical impulse to cause a heartbeat. But if you have what's called atrial tachycardia ( AT), an extra node in your atria is sparking electrical impulses. If you have more than one site sending out these pulses, it's called âmultifocal atrial tachycardia.â Most often, MAT is diagnosed only in people who have a major illness of the heart and lungs. It goes away once the underlying problem is treated. You might be diagnosed with fibrillation or flutter of the atria. In fibrillation, your atria start up many fast and random electrical signals. The chambers, rather than pumping in a coordinated way, constantly quiver when this happens. The result may result in a heart rate above 100 beats per minute. Atrial flutter is similar to fibrillation, but your heartbeats are often regular instead of chaotic. Your heart may still pump too fast, though. It's possible for people to have episodes of both fibrillation and flutter.