This is a plain language summary of a clinical research study called RAPID. The study looked at the potential for how safe and effective etripamil was at stopping an episode of rapid heartbeats in people with atrioventricularnodal-dependent supraventricular tachycardia (AV-node-dependent SVT). An episode is used to describe the period of time when a person experiences an abnormally very fast heartbeat. This was done by comparing an investigational drug called etripamil with a placebo, each administered via a rapidly acting nasal spray. AV-node-dependent SVT affects the rhythm of the heart, causing it to suddenly beat rapidly. The condition often requires medical treatment to help return the heart to its normal, healthy heartbeat pattern and speed, called 'sinus rhythm'. Researchers are looking at ways of improving the management of supraventricular tachycardias (SVT) by reducing the need for patients to attend an urgent care clinic, emergency ward or hospital for treatment. In the RAPID study, participants used a nasal spray containing either 70mg etripamil or a placebo solution when they experienced an episode of SVT. The researchers wanted to know how long it took for each participant's rapid heartbeat to return to sinus rhythm after administering the etripamil or placebo nasal spray. Participants in the study were considered successfully treated if their heartbeats returned to sinus rhythm for at least 30seconds within 30minutes of using the nasal spray. Although 30seconds may seem brief, it's medically important because it shows that a person's heartbeat has been temporarily stabilized and returned to normal functioning. Out of 99 people who used etripamil during an SVT episode, 63 participants (64%) experienced a return to sinus rhythm for at least 30seconds within 30minutes after using the nasal spray. In contrast, 26 out of 85 participants (31%) who used the placebo nasal spray experienced a return to sinus rhythm for at least 30seconds within 30minutes after use. Furthermore, the average time taken for the return to sinus rhythm was 17minutes for the etripamil group which was 3-times faster than the placebo group at 53minutes. Also, in the study no serious side effects occurred that were related to etripamil. The RAPID study supports the potential that etripamil may be safe and well tolerated by participants as a treatment for episodes of rapid heartbeat in people with AV-node-dependent SVT. The results also showed a significant improvement in symptoms following treatment with etripamil.