Background and objective The COVID‐19 pandemic has caused disruption to health, social interaction, travel and economies worldwide. In New Zealand, the government closed the border to non‐residents and required all arrivals to quarantine for 14 days. They also implemented a strict contact‐restriction system to eliminate COVID‐19 from the community. These measures also reduced the circulation of other respiratory viruses such as influenza and respiratory syncytial virus. We assessed the impact of these measures on hospital admissions for respiratory and cardiac diseases. Methods National data on hospital admissions for each week of 2020 were compared to admissions for the previous 5 years. Analyses were curtailed after week 33, when a COVID‐19 outbreak in Auckland led to different levels of pandemic restrictions making national data difficult to interpret. Results The numbers of acute infectious respiratory admissions were similar to previous years before the introduction of COVID‐19 restrictions, but then fell lower and remained low after the pandemic restrictions were eased. The usual winter peak in respiratory admissions was not seen in 2020. Other than small reductions during the period of the strictest contact restrictions, non‐infectious respiratory and cardiac admissions were similar to previous years and the usual winter peak in heart failure admissions was observed. Conclusion The observed patterns of hospital admissions in 2020 are compatible with the hypothesis that circulating respiratory viruses drive the normal seasonal trends in respiratory admissions. By contrast, these findings suggest that respiratory viruses do not drive the winter peak in heart failure. COVID‐19 pandemic restrictions in New Zealand led to marked reductions in circulating respiratory viruses and winter infectious respiratory admissions. There was little change in cardiac admissions, suggesting that respiratory viruses play a central role in seasonal respiratory admissions but not the winter peak in heart failure. See related Editorial