What is the correct electrode placement for a conventional ECG recording?

The electrode placement for a single-lead ECG recording is based on the Einthoven's Triangle (shown in the Figure below). Conventionally, recording Lead I is the most popular electrode configuration for a standard ECG recording and is as follows: positive electrode on left upper limb, negative electrode on the right upper limb, and ground electrode on the tail or on left lower leg.  

The most common electrode type used for rodent ECG is a needle electrode such as the MLA1213 Needle Electrodes while the MLA0313 Snap On Lead Wires with disposable, stick-on electrodes are popular for human ECG applications.

Note: Multi-lead ECG will require a more than one Bio-Amp channel.