Atrial Fibrillation: This is the most common type of arrhythmia, characterized by an irregular and often rapid heart rate, which can cause the sensation of heart quivering. It's a common condition, especially in older adults, and can be triggered by various factors including high blood pressure, heart valve problems, and thyroid issues.

Ventricular Premature Complexes (PVCs): These are early electrical impulses originating in the ventricles, causing the heart to contract prematurely. PVCs can create a sensation of skipped beats or quivering, especially if they occur frequently.
Anxiety or Panic Attacks: Anxiety can cause palpitations, which may feel like heart quivering. The physical symptoms of anxiety, including rapid heartbeat and tremors, can exacerbate the sensation.
Mitral Valve Prolapse: A condition where the two valve flaps of the mitral valve do not close smoothly or evenly, bulging (prolapse) upward into the left atrium when the heart contracts. It can cause palpitations, chest discomfort, and the sensation of heart quivering.

Cardiac Tamponade: A serious medical condition where fluid accumulates in the sac (pericardium) surrounding the heart, leading to compression of the heart. It can cause palpitations, chest pain, and shortness of breath, and is life-threatening if not promptly treated.
Pulmonary Embolism: A blockage of an artery in the lungs that can cause sudden and severe symptoms, including palpitations, chest pain, and shortness of breath. It's a medical emergency that requires immediate attention.
Hypertrophic Cardiomyopathy: A condition characterized by thickening of the heart muscle, which can lead to arrhythmias, including atrial fibrillation and ventricular tachycardia. It's a significant cause of sudden cardiac death in young athletes.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): A rare heart condition where the muscle in the right ventricle is replaced by fatty tissue, leading to arrhythmias and potentially sudden death.
Long QT Syndrome: A disorder of the heart's electrical activity that can cause sudden, uncontrollable, dangerous arrhythmias. It can be congenital or acquired due to various medications or conditions.
Brugada Syndrome: A genetic disorder characterized by abnormal electrocardiogram (ECG) findings and an increased risk of sudden cardiac death, often due to ventricular fibrillation.