The objective of this study is quantitatively analyze type I and III collagens in the papillary muscles of infarcted rats comparing them with a control group and carry out a immunohistochemical approach to assess the presence of types I, II, III, IV and VII collagens in the infarction scar region and in the rest of the myocardium. This study used 24 rats divided into two groups: infarcted and non-infarcted. After six weeks, the rats of both groups were killed in order to remove the anterior and posterior papillary muscles of the left ventricle. The material was observed under a light microscope, with polarization, to quantify, in percentage, types I and III collagens; one of the infarcted hearts was also randomly selected to undergo an immunohistochemical analysis to identify the presence of types I, II, III, IV and VII collagens in the post-infarction scar region and in the remaining myocardium. The anterior papillary muscles of the infarcted group presented a higher collagen concentration when compared with the control group; the means were found to be between 6.4 and 0.6% respectively. In posterior papillary muscle analysis, the mean for the infarcted group was 3.2 and 0.5% for the control group. Myocardial infarction leads to an increase in the concentrations of types I and III collagens in the anterior and posterior papillary muscles. Immunohistochemistry showed the presence of types I, II, III, IV and VII collagens in the infarction scar region and a lower amount of these same collagens in the rest of the myocardium.