In mitral stenosis, the left ventricular filling is reduced and the mitral valve is low in late diastole. Secondly, due to the reduced blood volume in the left ventricle, the systolic period is shortened accordingly. In complete atrioventricular block, the atrial and ventricular beats are unrelated, resulting in atrioventricular separation. When the atria and ventricles contract coupled simultaneously, the first heart sound is extremely loud, often referred to as the cannon sound. Diagnosis of apical 1st heart sound hyperactivity caused by rheumatic mitral stenosis: 1. Symptoms (1) Dyspnea caused by pulmonary venous hypertension and pulmonary stasis. In the early stage, it mostly appears during exercise, fever, pregnancy and other increases in cardiac blood output. As the disease progresses, dyspnea can occur with mild activity or even at rest. Dyspnea can also be triggered by increased ventricular rate during paroxysmal atrial fibrillation. (2) Hemoptysis is associated with rupture of small bronchial vessels due to long-term pulmonary venous hypertension. (3) Cough and hoarseness caused by extreme enlargement of the left atrium compressing the left main bronchus or laryngeal nerve. (4) Embolism of body circulation Heart failure and atrial fibrillation with corresponding clinical symptoms. (1) The first heart sound in the apical region of the heart is enhanced. The diastolic rumble-like murmur and open tapping sound (open valve sound) are typical signs of mitral stenosis. The interval between the second heart sound and the opening sound indicates the degree of mitral stenosis; the shorter the interval, the more severe the stenosis. The presence of a hyperactive first heart sound and an open valve sound suggests that the valve is reasonably elastic. Diastolic murmur loudness is not necessarily proportional to the degree of stenosis. In patients with mild to moderate stenosis, murmur loudness is directly proportional to the diastolic mitral transvalvular pressure step difference, with the more severe the stenosis the greater the pressure step difference and the louder the murmur. In patients with severe mitral stenosis, however, the murmur is reduced or even disappears, showing a “mute” mitral stenosis. There may be mild systolic elevated beats in the precordial region and diastolic tremors are often palpable in the apical region. (2) Mitral valve facies and jugular venous pressure elevation Severe mitral stenosis may present with mitral valve facies and jugular venous pressure elevation.