| Abnormality | Causes |
| Increased intensity | |
| Atrioventricular valve obstruction | |
| Mitral | Mitral stenosis and left atrial myxoma |
| Tricuspid | Tricuspid stenosis and right atrial myxoma |
| Increased transvalvular flow | |
| Mitral | Patent ductus arteriosus; ventricular septal defect; atrial septal defect |
| Tricuspid | |
| Forceful ventricular systole | Hyperkinetic heart syndrome; tachycardia (eg, exercise); mitral valve prolapse |
| Short PR interval | Pre-excitation syndrome; Lown-Ganong-Levine syndrome |
| Decreased intensity | |
| Immobility of mitral valve | Calcific mitral stenosis |
| Lack of apposition of the mitral leaflets | Rheumatic mitral regurgitation |
| Presystolic semiclosure of the atrioventricular valves | Long PR interval; acute aortic regurgitation; significant aortic stenosis; dilated cardiomyopathy |
| Conduction anomaly | Left bundle branch block |
| Wide splitting of S1 | |
| Conduction abnormalities | Complete right bundle branch block; left ventricular pacing; pre-excitation syndrome (left ventricular connection); Ebstein's anomaly |
| Mechanical | Tricuspid stenosis; atrial septal defect; Ebstein anomaly |
| Reversed splitting of S1 | |
| Arrhythmia | Premature beats (right ventricular origin) |
| Mechanical | Severe mitral stenosis and left atrial myxoma |
