A harsh, grade 4/6 systolic ejection (crescendo shaped) murmur that peaks at the end of systole (over the left sternal border in these 2 cats) is appreciated in this recording.
The murmurs of dynamic outflow tract obstruction are systolic murmurs heard best at the left or right heart base, depending on which outflow tract is obstructed (eg, left outflow tract best heard at left base). A left ventricular dynamic outflow tract obstruction is the most common cause of ejection murmurs in cats with hypertrophic cardiomyopathy; the murmur onset and duration coincide with systolic anterior motion of the mitral valve. The benign, physiologic murmur of the right ventricular dynamic outflow tract obstruction occurs commonly in cats at high heart rates and is not clinically significant.
Murmurs caused by dynamic ventricular outflow obstructions become louder as contraction strength and heart rates increase. An echocardiogram is necessary to determine whether a benign dynamic right ventricular outflow tract obstruction (DRVOTO) or a pathologic dynamic left ventricular outflow tract obstruction (DLVOTO) is causing the murmur.