Heart scores (the arithmetic mean of the QRS durations of the three bipolar limb leads for 10 cycles) and heart weights were determined from five draft type horses and five racing type horses, and evaluated for relationships between heart score and heart size within and between the two different types of horses. Horses were killed using a captive bolt gun, and actual heart weights were recorded using an electronic digital scale. The linear regression equation for heart weight versus heart score had a significant (P < 0.05) negative slope for racing types. The regression coefficients for heart weight versus heart score for draft types were not significantly (P > 0.05) different than zero. There was no significant (P > 0.05) difference found between draft and racing types. Significant (P < 0.01) differences were found between the heart ratios (heart weight as a percentage of live body weight) of racing and draft types. Heart scores were not found to be significantly (P > 0.05) different between racing and draft type horses.