Tachycardia is a medical condition characterized by an abnormally fast heart rate, typically defined as a resting heart rate exceeding 100 beats per minute. It can occur due to various factors, including stress, anxiety, fever, or underlying health issues such as heart disease or hyperthyroidism. There are different types of tachycardia, including atrial fibrillation and ventricular tachycardia, each with distinct causes and implications. While some cases may be harmless, others can lead to serious complications, making it essential to seek medical evaluation if symptoms like palpitations or dizziness occur.