This is the 8366th most frequent Japanese word.
心臓
Heart (the organ).
Here, '心臓' (heart) refers to the physical organ responsible for pumping blood.
彼の心臓は健康そのものだ。
His heart is in perfect health.
In this example, '心臓' figuratively represents the central emotional reaction of an individual.
驚きのニュースが彼の心臓を震わせた。
The surprising news shook his heart.
This usage of '心臓' denotes the anatomical heart as discussed in medical contexts.