To study cardiac function in an ovine model of chronic heart failure in relation to cardiac collagen and its phenotype, 11 sheep were developed into chronic heart failure by sequential microembolisation. Cardiac collagen contents and phenotypes were determined after hemodynamic evaluation at 6 months. The results showed that collagen contents and type Ⅰ /type Ⅲ collagen ratio in the left ventricle were increased significantly in heart failure group as compared with those in the normal group. Collagen concentration in left ventricle correlated significantly to left ventricular ejection fraction, left ventricular end diastolic pressure, dP/dt min , left ventricular diastolic diameter, and diastolic interventricular septum thickness.Our conclusion is increase in collagen content and type Ⅰ/Ⅲ collagen ratio may be partly responsible for the reduction of cardiac function seen in this model of heart failure.