An athletic 40-year-old man without a significant medical history was referred to the emergency department for episodes of palpitations. He had no cardiovascular risk factors and no family history of sudden death or cardiomyopathy. During the consultation, the patient was comfortable and afebrile, with a heart rate of 45 beats/min, respiratory rate of 12 beats/min, and blood pressure of 135/62 mm Hg. Physical examination revealed only a discrete pansystolic murmur at the left lower sternal border, which increased with inspiration. Routine blood test results were normal. His resting electrocardiogram (ECG) is shown in Figure 1A. He experienced recurrence of palpitations during several minutes while in the hospital, and a second ECG was recorded (Figure 1B). During this episode, the patient was hemodynamically stable, with no dyspnea or faintness. Transthoracic echocardiography revealed a normal left ventricle ejection fraction, no significant valvular heart disease, and apical dyskinesia of the right ventricle.