Acute heart failure and sudden death are possible outcomes of Trypanosoma cruzi infection in domestic dogs. Understanding which discrete typing units (DTUs) are present in fatal canine Chagas disease cases may help explain variation in disease outcome among infected dogs. We conducted a retrospective study of cases from the Texas A&M Veterinary Medical Diagnostic Laboratory and sampled heart tissue from 62 dogs with a histopathologic diagnosis of Chagas disease from 2007 to 2013 for which formalin-fixed paraffin embedded heart tissue was available. Extracted DNA was subjected to qPCRs for T. cruzi and DTU determination. Most dogs (63 %) were less than a year of age at time of death, and males and females were equally represented. Most cases died suddenly with clinical signs of less than one week or experienced sudden death with no prior clinical signs (79 %). Cardiac histopathology features included characteristic inflammation with cardiomyocyte degeneration +/- T. cruzi amastigotes. Lesions in other examined organs included hepatic congestion (37/47), pulmonary edema (24/40), and neuroinflammation (5/11), with T. cruzi amastigotes observed in the brain of one dog. Of 62 dog hearts sampled, DTU was determined in 34, with 33 TcI and one TcIV. Given vectors, wildlife, and dogs living with T. cruzi infections across Texas show both TcI and TcIV infections, this study provides evidence to support an association between TcI and fatal Chagasic heart disease in dogs, which may have prognostic relevance. More work is needed to better understand this association and understand the role of other DTUs circulating in the US.