The heart is a rather complex organ in humans and animals that works through the coordination of electrical pulses with muscle contraction. It beats due to synchronized contraction of myocytes initiated at the sino-atrial node through electrical action potentials that subsequently propagate through the heart. Cardiac arrhythmias are anomalies such as atrial and ventricular fibrillation, ventricular tachycardia, etc., that are generated through propagation disruption and instabilities in the electrical signals. We develop here general nonlinear models that describe the propagation of the action potentials through the heart tissue. As these signals propagate through the heart, they scan the various tissues that alter the specifics of their evolution in the different locations. The electrocardiogram gives a picture of this pulse propagation. The pseudo-electrocardiogram is a signal generated by the model pulses and contains only partial information compared to the one in a real clinical electrocardiogram.