An isometric ventricular preparation was used to investigate the effect of changes in temperature (10, 15, 20, 25 and 30 °C) on the cardiac contractility produced by increasing of frequency in the catfish heart. The ability of the ventricular preparation to develop the cardiac force at 10 °C continued regularly until a frequency of 1.0 Hz, whereas at 15, 20, 25 and 30 °C, it continued developing the cardiac force until 2.0 Hz. The contractile force, the rate of contraction and the rate of relaxation (cardiac contractions) decreased significantly as contraction frequency increased. The decreases in the cardiac contractility with the increasing of the contraction frequency from 0.2 to 2.0 Hz were significantly higher at 15, 20 and 25 °C than that at the same frequency at 30 °C and at 10 °C in the range of frequency between 0.2 and 1.0 Hz. The percentage changes in the contractile force at a contraction frequency of 2.0 Hz at 15, 20 and 25 °C were 42 ± 2.7, 32 ± 2.5 and 32 ± 3.3, respectively; whereas it was 61 ± 1.3 at 30 °C, and at 10 °C, it was 60 ± 1.1 at a frequency of 1.0 Hz. So, it can be concluded that the catfish myocardium, like most fish hearts exhibits a negative force–frequency relationship. But, this relationship is highly affected by the changes in the temperature in a way that the lower temperature (10 °C) and the higher temperature (30 °C), may provide a protective mechanism against the depressive effects of higher stimulation frequency. This may be due to the differences in the handling of the activator Ca2+ to the contractile system via the transsarcolemmal Ca2+ channels and/or Na+–Ca2+ changes, and the sarcoplasmic reticulum Ca2+ release.