In this paper, we study how the impact of a cyber attack that paralyzes the ability of one or more banks to send payments would be transmitted to other banks through the Canadian wholesale payment system. Based on historical payment data, we simulate a wide range of scenarios and evaluate the total payment disruption in the system. We find that, depending on the type and number of banks under attack, the time of the attack and the design of the payment system, an attack can in some cases quickly become systemic and result in a significant loss of liquidity in the system. For instance, a three-hour attack on one bank can in a worst-case scenario impair the payments capacity of seven other banks within less than an hour and eventually disrupt 25% of the daily payments value. We also demonstrate that the system-wide impact of an attack can be significantly reduced by contingency plans that enable attacked banks to continue to send high-value payments. Given the interconnectedness of banks, we conclude that the cyber resilience of a wholesale payment system strongly depends on the cyber resilience of its participants and we underline the importance of strong sectoral collaboration and coordination.