Supraventricular Tachycardia (SVT): This is the most likely diagnosis given the presentation, as SVT is a common condition characterized by an abnormally fast heart rate originating from a location above the ventricles, often presenting with sudden onset and termination.

Atrial Fibrillation: Although less likely than SVT, atrial fibrillation can present with a rapid heart rate and should be considered, especially in older patients or those with underlying heart disease.
Atrial Flutter: This condition can also cause a rapid heart rate and may be considered, particularly if the patient has a history of heart disease or recent cardiac surgery.
Sinus Tachycardia: While typically not as rapid as SVT, sinus tachycardia can be considered, especially if there's an underlying cause such as dehydration, anxiety, or fever.

Ventricular Tachycardia: Although less common than SVT, ventricular tachycardia is a life-threatening condition that requires immediate attention. It's crucial to distinguish it from SVT due to its potential for severe consequences, including cardiac arrest.
Wolff-Parkinson-White (WPW) Syndrome: This condition can cause SVT but may also lead to more dangerous arrhythmias. Identifying WPW syndrome is critical due to its potential for severe complications.
Hyperkalemia: While not a primary cardiac rhythm disorder, hyperkalemia can cause various arrhythmias, including those mimicking SVT. It's a condition that requires immediate treatment to prevent life-threatening complications.

Junctional Tachycardia: A rare condition where the heart's electrical impulse originates from the AV junction, leading to a rapid heart rate.
Mahaim Fiber Tachycardia: A rare type of SVT involving an accessory electrical pathway in the heart.
Lown-Ganong-Levine (LGL) Syndrome: A rare condition similar to WPW syndrome but with different characteristics, leading to SVT.