**Core Concept**
Cardiac muscle, a type of striated muscle, exhibits unique characteristics that distinguish it from skeletal and smooth muscle. Key features include the presence of T-tubules for efficient excitation-contraction coupling and the troponin system, which regulates muscle contraction.

**Why the Correct Answer is Right**
Caldesmon, a regulatory protein, is primarily associated with smooth muscle and plays a crucial role in the regulation of actin-myosin interaction. In contrast, cardiac muscle relies on the troponin-tropomyosin complex to regulate contraction. Caldesmon's absence in cardiac muscle highlights its distinct regulatory mechanisms. The troponin system, consisting of troponin C, troponin I, and troponin T, is essential for calcium-mediated contraction in cardiac muscle.

**Why Each Wrong Option is Incorrect**
**Option A:** Striated refers to the banded appearance of cardiac muscle under the microscope, which is a result of the regular arrangement of actin and myosin filaments. This characteristic is indeed a feature of cardiac muscle.
**Option B:** Large T-tubules are a hallmark of cardiac muscle, facilitating the efficient transmission of the action potential to the interior of the muscle fiber, where contraction is initiated.
**Option C:** The troponin system is present in cardiac muscle, playing a critical role in regulating contraction in response to changes in calcium ion concentration.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that cardiac muscle's unique regulatory mechanisms, including the troponin system, are crucial for its function and response to various pathological conditions, such as heart failure and cardiomyopathy.

**✓ Correct Answer: D. Caldesmon is important regulatory protein**